On Sun, 16 Jun 2019 20:40:34 +1000, Xeno wrote:

It does indeed! Same kind of feathering I'm getting on my Toyota's front
tyres - a feathering that you can easily feel in the early stages as you
run your hands for and aft along that section of tread area.

Thanks for that information, where the one correction I need to make is
that you can only feel this feathering running your hand "*backward*"
(clockwise) over the outside quarter of the tread pattern.
https://i.postimg.cc/zvvyL2tq/mount24.jpg

If you run your hand toward the front (counterclockwise), you can't feel
the feathering because each "lip" is downward.
https://i.postimg.cc/vTZLmZrN/mount25.jpg

When you run your hand toward the rear of the vehicle, each lip is upward.
https://i.postimg.cc/X7hcV3ps/mount26.jpg

That's the oddity. The feathering is only one way.
https://i.postimg.cc/KYhPMN7L/mount27.jpg

It's reproducible for years - so it's always the same.
That one-way lip feathering should be diagnostic, should it not?
https://i.postimg.cc/Wzyrb6bd/mount28.jpg

BTW, positive caster will accentuate the camber scrub. Caster is
generally not a tyre wearing angle. However, the more caster your
steering has, the more camber *change* you will get when turning the
steering.

Hmmmmmmmm.... maybe I can consider lessening positive caster a teeny bit?

Positive caster will give you a beneficial gain in terms of
handling. You will get more camber gain (more +ve) on the inside wheel
but the outside wheel will experience camber *loss* and become more
vertical or even negative. Since the more vertical tyre is on the
outside, the tread will get more grip with reduced slip angle aided by
weight transfer. This is great for cornering at speed. However when
travelling at slow speeds, weight transfer is not as significant and the
camber angle on the inside wheel, the one at the tightest lock, heads
towards positive extremes.

This is very useful information, as all our lock-to-lock cornering is at
30mph to 40mph ... never faster because I ran a test last week where
anything over 40mph is impossible to do even remotely safely, as all the
turns are blind turns and the file miles of 9% twisty road can't even be
twenty feet wide at the maximum (I should measure it but it's something
like that, as it's too narrow for the county to center stripe it legally).

It is, in effect, riding heavily on the outer
edge of the tread and this is where, and why, the damage is being done.

I need to study more - where your conclusion is spot on perfect but where I
don't get the individual steps only because I think of alignment as being
'static' so to speak. I know it changes - but my brain doesn't know 'how'
it changes under those slow speed lock-to-lock downhill (or uphill) turns.

The tread blocks have only so much flex before they are forced to break
contact with the road and slide. You've seen the evidence of what that does.

Yes. That's for sure. The outer tread blocks "feather" such that you can
feel it, and barely see it, after about 1000 miles. The only thing I can
do, is change the alignment or rotate every 1000 miles (but even rotation
won't stop it - it just evens it out with the rears).

Caster specifications are usually given as a range, say between 1 and 2
degrees with a side to side variation limit. All you can really do to
mitigate the effect is to set your caster to the low end of the
specified range.

That's EXACTLY what I'll do!
I have to admit I need to read, and re-read and re-read again what you
wrote above, as my brain needs to work in step-by-step fashion.

You didn't skip a step but I don't quite "believe" in my brain all the
steps, if you know what I mean. It's not that I don't believe you, but that
my brain has to understand EACH step before moving to the next step when it
comes to UNDERSTANDING why this happens. (It's kind of like a series of
math equations where I need to understand every step.)

On the other hand, once there is a conclusion, I can EXPERIMENT easily,
which is how a lot of cars get fixed (by throwing parts at the problems
without understanding them). So I will change the caster.

I have an alignment shop which runs a sale for $30 off to drop the $160
price to $130 who lessened my bimmer's rear camber from negative 2 degrees
to almost 0 degrees - where if I go to him - I can ask for the least caster
in the spec.

Better yet, I need to buy the tools to do that caster change myself - but
that's a topic for a different thread since I have to MEASURE it first.

On Sun, 16 Jun 2019 20:41:21 -0000 (UTC), "Arlen G. Holder"
wrote:

On Sun, 16 Jun 2019 20:40:34 +1000, Xeno wrote:

It does indeed! Same kind of feathering I'm getting on my Toyota's front
tyres - a feathering that you can easily feel in the early stages as you
run your hands for and aft along that section of tread area.

Thanks for that information, where the one correction I need to make is
that you can only feel this feathering running your hand "*backward*"
(clockwise) over the outside quarter of the tread pattern.
https://i.postimg.cc/zvvyL2tq/mount24.jpg

If you run your hand toward the front (counterclockwise), you can't feel
the feathering because each "lip" is downward.
https://i.postimg.cc/vTZLmZrN/mount25.jpg

When you run your hand toward the rear of the vehicle, each lip is upward.
https://i.postimg.cc/X7hcV3ps/mount26.jpg

That's the oddity. The feathering is only one way.
https://i.postimg.cc/KYhPMN7L/mount27.jpg

It's reproducible for years - so it's always the same.
That one-way lip feathering should be diagnostic, should it not?
https://i.postimg.cc/Wzyrb6bd/mount28.jpg

BTW, positive caster will accentuate the camber scrub. Caster is
generally not a tyre wearing angle. However, the more caster your
steering has, the more camber *change* you will get when turning the
steering.

Hmmmmmmmm.... maybe I can consider lessening positive caster a teeny bit?

Positive caster will give you a beneficial gain in terms of
handling. You will get more camber gain (more +ve) on the inside wheel
but the outside wheel will experience camber *loss* and become more
vertical or even negative. Since the more vertical tyre is on the
outside, the tread will get more grip with reduced slip angle aided by
weight transfer. This is great for cornering at speed. However when
travelling at slow speeds, weight transfer is not as significant and the
camber angle on the inside wheel, the one at the tightest lock, heads
towards positive extremes.

This is very useful information, as all our lock-to-lock cornering is at
30mph to 40mph ... never faster because I ran a test last week where
anything over 40mph is impossible to do even remotely safely, as all the
turns are blind turns and the file miles of 9% twisty road can't even be
twenty feet wide at the maximum (I should measure it but it's something
like that, as it's too narrow for the county to center stripe it legally).

It is, in effect, riding heavily on the outer
edge of the tread and this is where, and why, the damage is being done.

I need to study more - where your conclusion is spot on perfect but where I
don't get the individual steps only because I think of alignment as being
'static' so to speak. I know it changes - but my brain doesn't know 'how'
it changes under those slow speed lock-to-lock downhill (or uphill) turns.

The tread blocks have only so much flex before they are forced to break
contact with the road and slide. You've seen the evidence of what that does.

Yes. That's for sure. The outer tread blocks "feather" such that you can
feel it, and barely see it, after about 1000 miles. The only thing I can
do, is change the alignment or rotate every 1000 miles (but even rotation
won't stop it - it just evens it out with the rears).

Caster specifications are usually given as a range, say between 1 and 2
degrees with a side to side variation limit. All you can really do to
mitigate the effect is to set your caster to the low end of the
specified range.

That's EXACTLY what I'll do!
I have to admit I need to read, and re-read and re-read again what you
wrote above, as my brain needs to work in step-by-step fashion.

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

You didn't skip a step but I don't quite "believe" in my brain all the
steps, if you know what I mean. It's not that I don't believe you, but that
my brain has to understand EACH step before moving to the next step when it
comes to UNDERSTANDING why this happens. (It's kind of like a series of
math equations where I need to understand every step.)

On the other hand, once there is a conclusion, I can EXPERIMENT easily,
which is how a lot of cars get fixed (by throwing parts at the problems
without understanding them). So I will change the caster.

I have an alignment shop which runs a sale for $30 off to drop the $160
price to $130 who lessened my bimmer's rear camber from negative 2 degrees
to almost 0 degrees - where if I go to him - I can ask for the least caster
in the spec.

Better yet, I need to buy the tools to do that caster change myself - but
that's a topic for a different thread since I have to MEASURE it first.

On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.

On 17/6/19 6:41 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 20:40:34 +1000, Xeno wrote:

It does indeed! Same kind of feathering I'm getting on my Toyota's front
tyres - a feathering that you can easily feel in the early stages as you
run your hands for and aft along that section of tread area.

Thanks for that information, where the one correction I need to make is
that you can only feel this feathering running your hand "*backward*"
(clockwise) over the outside quarter of the tread pattern.
https://i.postimg.cc/zvvyL2tq/mount24.jpg

If you run your hand toward the front (counterclockwise), you can't feel
the feathering because each "lip" is downward.
https://i.postimg.cc/vTZLmZrN/mount25.jpg

When you run your hand toward the rear of the vehicle, each lip is upward.
https://i.postimg.cc/X7hcV3ps/mount26.jpg

That's the oddity. The feathering is only one way.
https://i.postimg.cc/KYhPMN7L/mount27.jpg

Not really. You are only driving in the one direction so the feathering
will only be in one direction. If it were in both directions, it
wouldn't be feathering, it would be *scalloping*, a diagnosis for a
different cause.

It's reproducible for years - so it's always the same.
That one-way lip feathering should be diagnostic, should it not?
https://i.postimg.cc/Wzyrb6bd/mount28.jpg

BTW, positive caster will accentuate the camber scrub. Caster is
generally not a tyre wearing angle. However, the more caster your
steering has, the more camber *change* you will get when turning the
steering.

Hmmmmmmmm.... maybe I can consider lessening positive caster a teeny bit?

You could experiment with it. After all, caster is not the only driver
of steering returnability but you need to be very judicious in doing so
noting that steering will be less precise, possibly more vague.
Regardless, any caster reduction will be only part of the story since
the primary cause, SAI, is well out of your control as it is a designed
in feature.

Positive caster will give you a beneficial gain in terms of
handling. You will get more camber gain (more +ve) on the inside wheel
but the outside wheel will experience camber *loss* and become more
vertical or even negative. Since the more vertical tyre is on the
outside, the tread will get more grip with reduced slip angle aided by
weight transfer. This is great for cornering at speed. However when
travelling at slow speeds, weight transfer is not as significant and the
camber angle on the inside wheel, the one at the tightest lock, heads
towards positive extremes.

This is very useful information, as all our lock-to-lock cornering is at
30mph to 40mph ... never faster because I ran a test last week where
anything over 40mph is impossible to do even remotely safely, as all the
turns are blind turns and the file miles of 9% twisty road can't even be
twenty feet wide at the maximum (I should measure it but it's something
like that, as it's too narrow for the county to center stripe it legally).

I was going to suggest you run wide arcs around the bends but it seems
that's not even possible.

It is, in effect, riding heavily on the outer
edge of the tread and this is where, and why, the damage is being done.

I need to study more - where your conclusion is spot on perfect but where I
don't get the individual steps only because I think of alignment as being
'static' so to speak. I know it changes - but my brain doesn't know 'how'
it changes under those slow speed lock-to-lock downhill (or uphill) turns.

It's what the tread is doing at the contact patch that is the critical
issue here and that is damn difficult to visualise. Start with the
forces acting on a tyre contact patch and you will see what I mean;

http://racingcardynamics.com/racing-...lateral-force/

In particular, this diagram;

http://racingcardynamics.com/wp-cont...10/Figure3.jpg

In your case, that contact patch centre of pressure will be off to the
outside and not even. See the curved path? No small wonder that tread
block deformation occurs.

Once I started to understand the forces creating slip angles, then I
began to get the bigger picture on tyre wear and, more importantly,
handling.
https://encrypted-tbn0.gstatic.com/i...7M7U1oj7bpK3ow

Again note the curved path through the contact patch while cornering.
That is the start point to understanding the concept as that is a result
of the combination of forces acting at that pint..

The tread blocks have only so much flex before they are forced to break
contact with the road and slide. You've seen the evidence of what that does.

Yes. That's for sure. The outer tread blocks "feather" such that you can
feel it, and barely see it, after about 1000 miles. The only thing I can
do, is change the alignment or rotate every 1000 miles (but even rotation
won't stop it - it just evens it out with the rears).

I am presented with that same fait acompli with my car. My case is not
as bad as yours as I get ~60,000 kilometres per set of tyres anyway,
even with camber scrub issues.

Caster specifications are usually given as a range, say between 1 and 2
degrees with a side to side variation limit. All you can really do to
mitigate the effect is to set your caster to the low end of the
specified range.

That's EXACTLY what I'll do!
I have to admit I need to read, and re-read and re-read again what you
wrote above, as my brain needs to work in step-by-step fashion.

You aren't Robinson Crusoe in that respect. It has taken me years to
come to the level of understanding of steering I now have. I have a
greater understanding of steering and handling now than had when I was
teaching the topic at a technical college. I have found traditional
texts on the topic aren't sufficient to give one the depth of
understanding required - seek instead engineering texts on the topic and
those devoted to motor racing. Those who work at the extremes of
handling seem to have a better idea of what's happening at that contact
patch.

You didn't skip a step but I don't quite "believe" in my brain all the

I probably did. There is a whole section there on what actually happens
when that tread passes through the contact patch. I cannot find a
suitable diagram that provides, in and of itself, a decent explanation
save for those on slip angle forces linked above because, as you have
noted, it is difficult to picture in your mind what is going on.

steps, if you know what I mean. It's not that I don't believe you, but that
my brain has to understand EACH step before moving to the next step when it
comes to UNDERSTANDING why this happens. (It's kind of like a series of
math equations where I need to understand every step.)

I know what you mean. It has taken me a long time and a lot of reading
about steering geometry before I had enough of an understanding how it
all works.

On the other hand, once there is a conclusion, I can EXPERIMENT easily,
which is how a lot of cars get fixed (by throwing parts at the problems
without understanding them). So I will change the caster.

A lot of cars have *money* wasted on them following that process. Far
better to understand system operation and then experiment around the
causes of the problem in order to effect a better *compromise* that
mitigates your issue. As has been noted, you will not likely be able to
cure your issue since it is a result of steering geometry compromise
favouring highway operation but you now have a more precise start point.

I have an alignment shop which runs a sale for $30 off to drop the $160
price to $130 who lessened my bimmer's rear camber from negative 2 degrees
to almost 0 degrees - where if I go to him - I can ask for the least caster
in the spec.

You might want to discuss with him your issue and why you want to change
the spec. Get him onside.

Better yet, I need to buy the tools to do that caster change myself - but
that's a topic for a different thread since I have to MEASURE it first.



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.

I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On Mon, 17 Jun 2019 15:01:47 +1000, Xeno wrote:

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?

Hi Xeno,
I'm sorry for causing confusion.

The feathering is on the OUTSIDE edge of both front tires.
https://i.postimg.cc/zvvyL2tq/mount24.jpg

If I said otherwise, it was my mistake.

Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that.

You can feel it on the edge of the tire closest to you when you stand next
to the tire, which is the OUTSIDE edge.

I apologize if I said otherwise.

I need to learn more about camber scrub in slow speed turns!

On 17/6/19 3:32 pm, Arlen G. Holder wrote:
On Mon, 17 Jun 2019 15:01:47 +1000, Xeno wrote:

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?

Hi Xeno,
I'm sorry for causing confusion.

The feathering is on the OUTSIDE edge of both front tires.
https://i.postimg.cc/zvvyL2tq/mount24.jpg

If I said otherwise, it was my mistake.

Well, I was misled by your words and Clare's on the topic of wear on
*both sides*.

Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that.

You can feel it on the edge of the tire closest to you when you stand next
to the tire, which is the OUTSIDE edge.

I apologize if I said otherwise.

No probs.

I need to learn more about camber scrub in slow speed turns!

Might I suggest that the first thing you look at is the contact patch
and, with it, slip angles. That will give you a great deal of insight
into what is happening down at that critical part of your tyre.

Once you study slip angles, some of the mysteries of suspension and
steering geometry will begin to unfold.

Here is an example.
No doubt you have heard of the Ackermann Angle. It is the one that
allows your inner and outer wheels to follow a different path on turns,
the inner being at a tighter radius. This explains it, sort of;

https://www.youtube.com/watch?v=oYMMdjbmQXc

The way he describes it, the line through both rear wheels is the
critical one.

This pic shows the same diagram plus the one showing how they achieve
the Ackermann Angle.

https://www.pinterest.com.au/pin/185843922100707086/

The steering arms are inclined inwards so that the intersect point, the
turning centre, is at the centre of the rear axle. The problem is - no
car is built this way. When I was an apprentice, we were taught this
principle. Some diagrams were shown as above, some were shown with the
intersect point somewhat further forward of the rear axle and along the
centreline. No explanation was given back then for this difference. The
intersect point at the rear axle centreline works *if* you neglect slip
angle - as Ackermann quite obviously did. Given that the patent was
filed in 1818 and was intended for horse drawn vehicles, it likely
worked well enough in that situation, especially given wheels typically
had iron rims.

When slip occurs at the tyre contact patches, the *turning centre* will
move forward. The extent of this move forward will be dependent on the
relationship between the slip angles front and rear. High cornering
forces create roll and demand greater slip angles from the outer tyres
than the inner. Ackermann's principle then was based on a false premise.
Vehicles use what is known as a *modified Ackermann*.

To better understand this you need to delve into slip angles and then
progress to the dynamic handling of a vehicle when cornering. It gets
very complicated when you start looking at the geometry of the various
suspension systems. Some rear suspensions, for instance, create *toe in*
at the outer rear wheel under body roll. This has an effect on slip
angles and counters oversteer.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On Mon, 17 Jun 2019 15:01:47 +1000, Xeno
wrote:

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.


Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI. When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is he
https://www.hotrod.com/articles/camb...tire-traction/.
It is slanted towards circle track racing, but covers all the basics.


I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.

On Tue, 18 Jun 2019 00:44:17 +1000, Xeno wrote:

Might I suggest that the first thing you look at is the contact patch
and, with it, slip angles. That will give you a great deal of insight
into what is happening down at that critical part of your tyre.

Hi Xeno,
THANK YOU for that suggestion to concentration on understanding the
dynamics of the contact patch first in hard downhill cornering.

I have to admit that I've read (and re-read) what you've written, but it's
like a series of math equations, where I can only grasp the starting point
and the ending point - but I can't make the connection to each of the
interim equations.

What makes things infinitely worse is that, as you're aware, I only care
about the slow-speed 20 to 35mph mostly) downhill (mostly) lock-to-lock
cornering forces that are causing the unidirectional feathering on the
outside corner.

There's precious little on the net about that specific problem, where,
everything I read seems to be about high speed racing with much greater
radii corners, which just isn't what's going on here.

I said before our corners are 180 degrees and 270 degrees where I realized
belatedly that none are 270 degrees, but many are 90 degrees (and, in fact,
most are 90 degrees) where about 1/10th are 180 degree hairpins.

Interestingly, I noticed that the hairpins all have a "pullout area" (for
trucks, I guess, which always back up forward and backward for a few tries
before they can make the turn).

So we "can" take a hairpin wide but only if the direction we're going has
the pullout, as the pullouts are always in the uphill side of the road,
which can be on either side of the road depending on the switchback.

Once you study slip angles, some of the mysteries of suspension and
steering geometry will begin to unfold.

Again, thank you for suggesting a way for my brain to begin to grasp the
singular problem.

Do you agree with my assessment that downhill is worse than uphill?

And, is the outside tire (the tire furthest from the center of the curve)
the tire that wears most from this feather scrubbing?

Clare Snyder posted for all of us...



On Fri, 14 Jun 2019 14:51:53 -0400, Tekkie®
wrote:

Clare Snyder posted for all of us...



On Wed, 12 Jun 2019 05:52:33 -0000 (UTC), "Arlen G. Holder"
wrote:

Clare - are smaller car tires easier to balance than SUV tires?
https://i.postimg.cc/kG1M7cLd/mount15.jpg

A neighbor was in need of tires who knew that I had bought a few extra for
her long ago where they've been sitting outside in the rain & mud for
months waiting for her to need them.
https://i.postimg.cc/7L8HPbtb/mount16.jpg

She finally wore through the belts and had to stop over for an "emergency"
tire change, which I did for her, but she was in a rush so we did it in
about 20 minutes from start to finish.

I had to do it so fast that I didn't see the yellow dot until I looked at
this picture, where I mounted the red dot to the valve stem instead of the
yellow dot as you had recommended for when there are no match mounting
marks.

I did statically balance and she reported no vibration whatsoever. I didn't
spend a lot of time cleaning up things so I'm surprised there's no
imbalance given how quickly I did the job for her.

Just wondering if you've found that these tiny 14-inch tires are a piece of
cake compared to the normal truck SUV tires (like the Optimo's that I'm
used to) both in terms of mounting and balancing?


Yes and no. The smaller tire has less total mass so a small amount
of weight has more effect than it would on a bigger tire - but it is
not as far from the center (shorter moment arm) so it has less effect.

GOOD tires of any size are easier to ballance than crappy tires. Ealy
Hankooks were a real pain to ballance. Apparentlythey have gotten
better.

I had a set of early Hankooks and could not get rid of the vibration. IIRC I
got Conti's with very good results.
Could never figure out exactly how many corners Hankook figured
there were in a circle - - - -

Good one!

--
Tekkie

Clare Snyder posted for all of us...



However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.


+1 Keep the contact area against the pavement.

--
Tekkie

On 18/6/19 6:06 am, Tekkie® wrote:
Clare Snyder posted for all of us...



However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.


+1 Keep the contact area against the pavement.

That assumes the tyre starts out vertical with respect to the road. In
the case of camber scrub, the tyre on the inside of the turn is going to
extreme positive camber angles whereas the tyre on the outside *loses*
camber and becomes more vertical. that means the outside tyre sits more
flat on the road. The inside tyre, on the other hand, has gained camber
and is riding hard on its outer tread edge. The above scenario, with the
tyres *aired up*, keeps the tyre rigid and applies *more pressure
(force)* to the outside edge that is already in heavy contact with the
road. The centre of the tread is where most of the deflection occurs as
you increase the pressure - most with crossply tyres, least with steel
belted radials. Why do you think it is that radial tyres have minimal
static camber angles? It is because they naturally sit flatter on the
road with sidewall deformation rather than tread area deformation.
Another aspect is that weight transfer is negligible in slow speed
cornering and even if it were, that would still mean that the inside
tyre still gets scuffing because the load gets reduced and tread slip
occurs earlier than if the tread blocks were forced to maintain contact
longer. The inside tyre is the one at the extreme camber angle. If it's
a radial or, more so, a steel belted radial, it is designed to operate
with minimal camber.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On 18/6/19 12:58 am, Clare Snyder wrote:
On Mon, 17 Jun 2019 15:01:47 +1000, Xeno
wrote:

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.


Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI.

Are you sure about that? SAI is, after all, Steering Axis Inclination.

If we are talking about a *King Pin* in a beam axle arrangement, the KPI
angle is absolutely fixed and cannot be altered without recourse to
*bending* something.

In terms of modern cars, however, king pins are obsolete. The last
vehicle I can recall working on that had king pins was mid 60s.

What we use now are, as you know, ball joints to anchor the steering
knuckle yet allow multi-degree articulation. Makes the kinematics a damn
sight easier to work out from the engineer's design viewpoint.

https://www.freeasestudyguides.com/g...clination..png

In the diagram above, there is a line referencing *true vertical*,
another referencing the SAI *angle*, and another referencing the tyre
camber angle. The *included angle* cannot be altered. It is designed in
and the only way to change that would be to *bend something*. In this
case, that something would be the steering knuckle. Definitely not
recommended but something that used to be done in vehicles of the 50s
and 60s when you ran out of adjustment. I was fortunate I never needed
to do that.

Looking at the linked diagram, if I feel the camber angle is too great,
what options do I have. I have to move one of the ball joints in
relation to the other. Assume the adjustment for camber is shims at the
inner end of the top control arm. So I set to and remove sufficient
shims to move upper control arm, including the upper ball joint, inwards
and change the *camber angle*, say, 1 degree to the negative. That means
I have now *reduced* by 1 degree the angle between the true vertical and
centreline of the tyre. The tyre is now more vertical than it was.
But, if I cannot change the *included angle*. I must also have also
*increased* the angle between the true vertical and the *steering axis*
through the ball joints. That 1 degree of angle didn't just disappear,
it simply moved to the other side of that line that represents true
vertical. That means I have *increased* the steering axis *inclination*
from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
it will now be 10 degrees.

What can we see from this? The wheel will be more vertical, no doubt,
since we have reduced camber. But, because the steering axis inclination
has increased, we will likely experience heavier steering. That may or
may not be noticeable. The vehicle will have more steering self
centering. Also, we are likely to get more of a camber change on the
inner wheel when the steering turns to either lock. Remember, positive
caster is playing a role in this camber change too. Will it matter? I
can't say because I have always worked within manufacturers
specifications and I can't readily visualise the kinematics of it.

The one thing you will almost certainly have done is changed the slip
angles at the front wheels because that is what camber changes to the
negative at the front wheels do. That will have, in turn, altered the
oversteer/understeer balance between the front and rear of the vehicle.
Vehicles are given positive camber at the front wheels and zero or
negative camber at the rear. That promotes understeer, a safer situation
for the average driver. By reducing caster to the minimum spec, you will
achieve a similar outcome with regard to tyre wear but will not be
dicking with the handling balance.

When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is he
https://www.hotrod.com/articles/camb...tire-traction/.
It is slanted towards circle track racing, but covers all the basics.

Yes, but it covers all the basics with a distinct *bias*. For someone
who wants to learn about the basics, it is best they look at what is
done for *road going cars* first. It is a different world with regard to
handling. Sure, progress to racing cars but do get the basics down pat
first.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.


I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On Wed, 19 Jun 2019 00:17:29 +1000, Xeno
wrote:

On 18/6/19 12:58 am, Clare Snyder wrote:
On Mon, 17 Jun 2019 15:01:47 +1000, Xeno
wrote:

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.


Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI.

Are you sure about that? SAI is, after all, Steering Axis Inclination.


100%
KPI or SAI is also known as the "included angle" and is the angle
between the centerline of the steering axis and the centerline of the
wheel axis (or spindle) Without bending the pdindle assembly it
cannot be changed on modern vehicles. On older AMC and a few others
with bolt-on spindles (including SOME current FWD vehicles you CAN
change the SAI somewhat by inserting tapered shims between the knuckle
and the spindle. MOST RWD cars and a large number of FWD today do NOT
use a bolt-on spindle or a bolt-on bearing housing, making it
impossible. On the 2 part knuckles (separate knuckle and spindle) we
used to occaisionally shim them for" competition"

If we are talking about a *King Pin* in a beam axle arrangement, the KPI
angle is absolutely fixed and cannot be altered without recourse to
*bending* something.

What are you thinking of bending?

In terms of modern cars, however, king pins are obsolete. The last
vehicle I can recall working on that had king pins was mid 60s.

What we use now are, as you know, ball joints to anchor the steering
knuckle yet allow multi-degree articulation. Makes the kinematics a damn
sight easier to work out from the engineer's design viewpoint.

https://www.freeasestudyguides.com/g...clination..png

In the diagram above, there is a line referencing *true vertical*,
another referencing the SAI *angle*, and another referencing the tyre
camber angle. The *included angle* cannot be altered. It is designed in
and the only way to change that would be to *bend something*. In this
case, that something would be the steering knuckle. Definitely not
recommended but something that used to be done in vehicles of the 50s
and 60s when you ran out of adjustment. I was fortunate I never needed
to do that.


I never bent a spindle, but the flamboprough hobby stock car guys did
sometimes. It was easier to use an AMC knuckle and just shim it - no
worrying about if you got the heat treat right -- - -
Looking at the linked diagram, if I feel the camber angle is too great,
what options do I have. I have to move one of the ball joints in
relation to the other. Assume the adjustment for camber is shims at the
inner end of the top control arm. So I set to and remove sufficient
shims to move upper control arm, including the upper ball joint, inwards
and change the *camber angle*, say, 1 degree to the negative. That means
I have now *reduced* by 1 degree the angle between the true vertical and
centreline of the tyre. The tyre is now more vertical than it was.
But, if I cannot change the *included angle*. I must also have also
*increased* the angle between the true vertical and the *steering axis*
through the ball joints. That 1 degree of angle didn't just disappear,
it simply moved to the other side of that line that represents true
vertical. That means I have *increased* the steering axis *inclination*
from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
it will now be 10 degrees.

No - SAI IS the included angle.
Camber IS the deviation from true vertical
SAI is measured from the spindle centerline to the steering axis and
does NOT change, even if the car is laying on it's side. You get
CAMBER CHANGE with roll and squat - but you do NOT get SAI change.

What can we see from this? The wheel will be more vertical, no doubt,
since we have reduced camber. But, because the steering axis inclination
has increased, we will likely experience heavier steering. That may or
may not be noticeable. The vehicle will have more steering self
centering.

How?

Take a good look at the Turnolgy site for some good explanations.

https://www.turnology.com/tech-stori...ke-you-faster/

Also, we are likely to get more of a camber change on the
inner wheel when the steering turns to either lock. Remember, positive
caster is playing a role in this camber change too. Will it matter? I
can't say because I have always worked within manufacturers
specifications and I can't readily visualise the kinematics of it.

The one thing you will almost certainly have done is changed the slip
angles at the front wheels because that is what camber changes to the
negative at the front wheels do. That will have, in turn, altered the
oversteer/understeer balance between the front and rear of the vehicle.
Vehicles are given positive camber at the front wheels and zero or
negative camber at the rear. That promotes understeer, a safer situation
for the average driver. By reducing caster to the minimum spec, you will
achieve a similar outcome with regard to tyre wear but will not be
dicking with the handling balance.

When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is he
https://www.hotrod.com/articles/camb...tire-traction/.
It is slanted towards circle track racing, but covers all the basics.

Yes, but it covers all the basics with a distinct *bias*. For someone
who wants to learn about the basics, it is best they look at what is
done for *road going cars* first. It is a different world with regard to
handling. Sure, progress to racing cars but do get the basics down pat
first.

This IS a "handling" issue To be wearing the tires the way they are
being worn the vehicle is operating at the ragged edge of it's
handling capability on those carving downhills.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control
arm suspension, and it handled like it was on rails . With the wide
Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

Vehicles with strut suspension require MORE negative static camber to
compensate effectively for cornering camber change




I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.

On 2019-06-18 11:27 a.m., Clare Snyder wrote:
On Wed, 19 Jun 2019 00:17:29 +1000, Xeno
wrote:

On 18/6/19 12:58 am, Clare Snyder wrote:
On Mon, 17 Jun 2019 15:01:47 +1000, Xeno
wrote:

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.


Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI.

Are you sure about that? SAI is, after all, Steering Axis Inclination.


100%
KPI or SAI is also known as the "included angle" and is the angle
between the centerline of the steering axis and the centerline of the
wheel axis (or spindle) Without bending the pdindle assembly it
cannot be changed on modern vehicles. On older AMC and a few others
with bolt-on spindles (including SOME current FWD vehicles you CAN
change the SAI somewhat by inserting tapered shims between the knuckle
and the spindle. MOST RWD cars and a large number of FWD today do NOT
use a bolt-on spindle or a bolt-on bearing housing, making it
impossible. On the 2 part knuckles (separate knuckle and spindle) we
used to occaisionally shim them for" competition"

If we are talking about a *King Pin* in a beam axle arrangement, the KPI
angle is absolutely fixed and cannot be altered without recourse to
*bending* something.

What are you thinking of bending?

In terms of modern cars, however, king pins are obsolete. The last
vehicle I can recall working on that had king pins was mid 60s.

What we use now are, as you know, ball joints to anchor the steering
knuckle yet allow multi-degree articulation. Makes the kinematics a damn
sight easier to work out from the engineer's design viewpoint.

https://www.freeasestudyguides.com/g...clination..png

In the diagram above, there is a line referencing *true vertical*,
another referencing the SAI *angle*, and another referencing the tyre
camber angle. The *included angle* cannot be altered. It is designed in
and the only way to change that would be to *bend something*. In this
case, that something would be the steering knuckle. Definitely not
recommended but something that used to be done in vehicles of the 50s
and 60s when you ran out of adjustment. I was fortunate I never needed
to do that.


I never bent a spindle, but the flamboprough hobby stock car guys did
sometimes. It was easier to use an AMC knuckle and just shim it - no
worrying about if you got the heat treat right -- - -
Looking at the linked diagram, if I feel the camber angle is too great,
what options do I have. I have to move one of the ball joints in
relation to the other. Assume the adjustment for camber is shims at the
inner end of the top control arm. So I set to and remove sufficient
shims to move upper control arm, including the upper ball joint, inwards
and change the *camber angle*, say, 1 degree to the negative. That means
I have now *reduced* by 1 degree the angle between the true vertical and
centreline of the tyre. The tyre is now more vertical than it was.
But, if I cannot change the *included angle*. I must also have also
*increased* the angle between the true vertical and the *steering axis*
through the ball joints. That 1 degree of angle didn't just disappear,
it simply moved to the other side of that line that represents true
vertical. That means I have *increased* the steering axis *inclination*
from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
it will now be 10 degrees.

No - SAI IS the included angle.
Camber IS the deviation from true vertical
SAI is measured from the spindle centerline to the steering axis and
does NOT change, even if the car is laying on it's side. You get
CAMBER CHANGE with roll and squat - but you do NOT get SAI change.

What can we see from this? The wheel will be more vertical, no doubt,
since we have reduced camber. But, because the steering axis inclination
has increased, we will likely experience heavier steering. That may or
may not be noticeable. The vehicle will have more steering self
centering.

How?

Take a good look at the Turnolgy site for some good explanations.

https://www.turnology.com/tech-stori...ke-you-faster/

Also, we are likely to get more of a camber change on the
inner wheel when the steering turns to either lock. Remember, positive
caster is playing a role in this camber change too. Will it matter? I
can't say because I have always worked within manufacturers
specifications and I can't readily visualise the kinematics of it.

The one thing you will almost certainly have done is changed the slip
angles at the front wheels because that is what camber changes to the
negative at the front wheels do. That will have, in turn, altered the
oversteer/understeer balance between the front and rear of the vehicle.
Vehicles are given positive camber at the front wheels and zero or
negative camber at the rear. That promotes understeer, a safer situation
for the average driver. By reducing caster to the minimum spec, you will
achieve a similar outcome with regard to tyre wear but will not be
dicking with the handling balance.

When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is he
https://www.hotrod.com/articles/camb...tire-traction/.
It is slanted towards circle track racing, but covers all the basics.

Yes, but it covers all the basics with a distinct *bias*. For someone
who wants to learn about the basics, it is best they look at what is
done for *road going cars* first. It is a different world with regard to
handling. Sure, progress to racing cars but do get the basics down pat
first.

This IS a "handling" issue To be wearing the tires the way they are
being worn the vehicle is operating at the ragged edge of it's
handling capability on those carving downhills.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control
arm suspension, and it handled like it was on rails . With the wide
Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

Vehicles with strut suspension require MORE negative static camber to
compensate effectively for cornering camber change




I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.


have you ever tried just driving the car

On 19/6/19 4:27 am, Clare Snyder wrote:
On Wed, 19 Jun 2019 00:17:29 +1000, Xeno
wrote:

On 18/6/19 12:58 am, Clare Snyder wrote:
On Mon, 17 Jun 2019 15:01:47 +1000, Xeno
wrote:

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.


Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI.

Are you sure about that? SAI is, after all, Steering Axis Inclination.


100%
KPI or SAI is also known as the "included angle" and is the angle
between the centerline of the steering axis and the centerline of the
wheel axis (or spindle) Without bending the pdindle assembly it
cannot be changed on modern vehicles. On older AMC and a few others
with bolt-on spindles (including SOME current FWD vehicles you CAN
change the SAI somewhat by inserting tapered shims between the knuckle
and the spindle. MOST RWD cars and a large number of FWD today do NOT
use a bolt-on spindle or a bolt-on bearing housing, making it
impossible. On the 2 part knuckles (separate knuckle and spindle) we
used to occaisionally shim them for" competition"

If we are talking about a *King Pin* in a beam axle arrangement, the KPI
angle is absolutely fixed and cannot be altered without recourse to
*bending* something.

What are you thinking of bending?

In terms of the beam axle arrangement, I can see nothing that I could
satisfactorily bend in order to correct a KPI angle but, for KPI to be
out, something has to have been *bent*.

In terms of modern cars, however, king pins are obsolete. The last
vehicle I can recall working on that had king pins was mid 60s.

What we use now are, as you know, ball joints to anchor the steering
knuckle yet allow multi-degree articulation. Makes the kinematics a damn
sight easier to work out from the engineer's design viewpoint.

https://www.freeasestudyguides.com/g...clination..png

In the diagram above, there is a line referencing *true vertical*,
another referencing the SAI *angle*, and another referencing the tyre
camber angle. The *included angle* cannot be altered. It is designed in
and the only way to change that would be to *bend something*. In this
case, that something would be the steering knuckle. Definitely not
recommended but something that used to be done in vehicles of the 50s
and 60s when you ran out of adjustment. I was fortunate I never needed
to do that.


I never bent a spindle, but the flamboprough hobby stock car guys did
sometimes. It was easier to use an AMC knuckle and just shim it - no
worrying about if you got the heat treat right -- - -

There was, IIRC, a limit to the number of degrees you could bend a
steering component *without* the application of heat. The application of
heat is always a worry because, if you get it wrong, well, **** happens.

Looking at the linked diagram, if I feel the camber angle is too great,
what options do I have. I have to move one of the ball joints in
relation to the other. Assume the adjustment for camber is shims at the
inner end of the top control arm. So I set to and remove sufficient
shims to move upper control arm, including the upper ball joint, inwards
and change the *camber angle*, say, 1 degree to the negative. That means
I have now *reduced* by 1 degree the angle between the true vertical and
centreline of the tyre. The tyre is now more vertical than it was.
But, if I cannot change the *included angle*. I must also have also
*increased* the angle between the true vertical and the *steering axis*
through the ball joints. That 1 degree of angle didn't just disappear,
it simply moved to the other side of that line that represents true
vertical. That means I have *increased* the steering axis *inclination*
from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
it will now be 10 degrees.

No - SAI IS the included angle.

Please, be informed that SAI is the angle through the steering axis
relative to the *true vertical*. The true vertical is the *vertical
reference*, an imaginary line drawn at right angles to the road surface.
It will always *remain* at right angles to the road surface regardless
of what is done to the SAI *angle* and/or the camber angle. The
*included angle*, by its very name, *includes* the SAI angle *and* the
camber angle. The included angle is designed in and cannot be changed by
normal means. The included angle is a diagnosis angle and, if deviated
from specifications, indicates that the steering knuckle has suffered
damage, ie bent steering knuckle.

https://www.waybuilder.net/free-ed/S...s/09AdvW69.jpg

Do not be deceived by the angle at which the stub axle is drawn on the
above linked diagram. To be true to reality, the stub axle should have
been drawn at right angles to the blue centreline of the *wheel*. The
dotted blue line is not referencing anything on that diagram apart from
the horizontal datum line representing the road.

Camber IS the deviation from true vertical

We agree on one point at least. Yes, camber is the deviation from true
vertical. What we have, however, is a dispute regarding true vertical
and what it is referencing.

SAI is measured from the spindle centerline to the steering axis and

Correction, it not a reference to the spindle centreline, it is
referencing true vertical. The only point that doesn't change is the
true vertical since it is a vertical reference to the ground upon which
the vehicle is sitting and is at a *right angle* to it.

does NOT change, even if the car is laying on it's side. You get
CAMBER CHANGE with roll and squat - but you do NOT get SAI change.

If any steering axis *pivot* point moves laterally in relation to the
other pivot point, there will be a change in SAI relative to the true
vertical. There simply has to be. The included angle, since it is
*fixed* by design, cannot change. IOW, the angular relationship the
steering axis has with the camber angle is permanently fixed. The
included angle's relationship with the true vertical, however, is not fixed.



What can we see from this? The wheel will be more vertical, no doubt,
since we have reduced camber. But, because the steering axis inclination
has increased, we will likely experience heavier steering. That may or
may not be noticeable. The vehicle will have more steering self
centering.

How?

Any increase in SAI causes a commensurate increase in steering self
centering.

Take a good look at the Turnolgy site for some good explanations.

https://www.turnology.com/tech-stori...ke-you-faster/

We aren't looking at camber making a car faster. We are looking at
camber, under the influence of positive caster, making tyres wear on the
outside edge under severe steering lock situations at *low speed*.

Also, we are likely to get more of a camber change on the
inner wheel when the steering turns to either lock. Remember, positive
caster is playing a role in this camber change too. Will it matter? I
can't say because I have always worked within manufacturers
specifications and I can't readily visualise the kinematics of it.

The one thing you will almost certainly have done is changed the slip
angles at the front wheels because that is what camber changes to the
negative at the front wheels do. That will have, in turn, altered the
oversteer/understeer balance between the front and rear of the vehicle.
Vehicles are given positive camber at the front wheels and zero or
negative camber at the rear. That promotes understeer, a safer situation
for the average driver. By reducing caster to the minimum spec, you will
achieve a similar outcome with regard to tyre wear but will not be
dicking with the handling balance.

When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is he
https://www.hotrod.com/articles/camb...tire-traction/.
It is slanted towards circle track racing, but covers all the basics.

Yes, but it covers all the basics with a distinct *bias*. For someone
who wants to learn about the basics, it is best they look at what is
done for *road going cars* first. It is a different world with regard to
handling. Sure, progress to racing cars but do get the basics down pat
first.

This IS a "handling" issue To be wearing the tires the way they are
being worn the vehicle is operating at the ragged edge of it's
handling capability on those carving downhills.

Um, no it is not. It is entirely *normal* given the nature of the
vehicle operation. Let me excerpt a snippet from an old text I used to
use when teaching this stuff;

Caster Angle Tire Wear
The caster angle is generally considered to be a nontire wearing angle.
Although this statement is true, unequal or *excessive* caster can
*indirectly* cause tire wear. When the front wheels are turned on a
vehicle with a lot of positive caster, the front wheels become angled,
called camber *roll*. (The caster angle is a measurement of the
difference in camber angle from when the wheel is turned inward to when
the wheel is turned outward.) Many vehicle manufacturers have positive
caster designed into the suspension system. This positive caster has
increased the directional stability of these vehicles. However, if the
vehicle is used exclusively in city-type driving, the positive caster
can cause wear to the outside shoulders of both front tyres.
Automotive Chassis Systems, Brakes, Steering, Suspension and Alignment
James D. Halderman, 1996, Prentice Hall Inc.

This text is in full agreement with my diagnosis of Arlen's issue. His
issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
evidenced by the specific type of longitudinal feathering he is
experiencing on the outer shoulder of his tyres. It also supports the
partial solution that I offered, that he reduce his caster to the
minimum allowable specification. I have *known* of this issue for
*decades* but my current Toyota has given me my first personal
experience with it.


For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control

Negative caster is unusual on a RWD car since it has the nasty effect of
increasing body roll, highly undesirable. Negative caster is more usual
on a FWD because of drive torque as opposed to rolling resistance but it
is kept to a bare minimum. It would be interesting to see all the
steering geometry specifications for that vehicle.

arm suspension, and it handled like it was on rails . With the wide

I presume you mean SLA front suspension.

Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

That will depend entirely on the type of driving you do. If it's a lot
of highway driving, no problem. Light urban driving, again no problem.
Our previous Toyota didn't show an issue but it was in an urban
environment most of its life. If you have lots of tight turns, as I have
experienced here and Arlen has experienced, you get camber scrub. It is
the compromise the manufacturers had to make given typical vehicle usage
patterns. Arlen's usage is not typical since he is doing lots of full
lock turns, grade notwithstanding. It is the full lock turns, with
attendant high positive camber gain on the inner wheel, that do the damage.

Vehicles with strut suspension require MORE negative static camber to
compensate effectively for cornering camber change




I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On Wed, 19 Jun 2019 13:26:36 +1000, Xeno wrote:

We aren't looking at camber making a car faster. We are looking at
camber, under the influence of positive caster, making tyres wear on the
outside edge under severe steering lock situations at *low speed*.

Hi Xeno,
I agree with this special case, which most descriptions on the net ignore
since they're looking at racing versus nominally around 30mph.

Today I counted the steering wheel degrees, where on many turns it was only
90 degrees to the left and 90 degrees to the right, and on plenty others it
was 180 to the left or right, and on about 10% of the turns, it was more
than 360, where the biggest turns were more than 360 plus 90, and the less
biggest turns were slightly less than that, at about 375 degrees turning
the steering wheel.

I also hung a redneck lateral 'accelerometer' on the mirror, which was
simply the USB cable for the phone looped over the mirror, where it swung
from side to side constantly, but at about 45 degrees or less most of the
time. https://i.postimg.cc/L6CN5SKm/mount30.jpg

While it was hard to snap photos since one hand had to be on the steering
wheel, I had expected the loop of USB cable to swing further than 45
degrees but most of the time it seemed LESS than 45 degrees, I guess
because the speeds are so slow?

On Wed, 19 Jun 2019 13:26:36 +1000, Xeno
wrote:

On 19/6/19 4:27 am, Clare Snyder wrote:
On Wed, 19 Jun 2019 00:17:29 +1000, Xeno
wrote:

On 18/6/19 12:58 am, Clare Snyder wrote:
On Mon, 17 Jun 2019 15:01:47 +1000, Xeno
wrote:

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.


Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI.

Are you sure about that? SAI is, after all, Steering Axis Inclination.


100%
KPI or SAI is also known as the "included angle" and is the angle
between the centerline of the steering axis and the centerline of the
wheel axis (or spindle) Without bending the pdindle assembly it
cannot be changed on modern vehicles. On older AMC and a few others
with bolt-on spindles (including SOME current FWD vehicles you CAN
change the SAI somewhat by inserting tapered shims between the knuckle
and the spindle. MOST RWD cars and a large number of FWD today do NOT
use a bolt-on spindle or a bolt-on bearing housing, making it
impossible. On the 2 part knuckles (separate knuckle and spindle) we
used to occaisionally shim them for" competition"

If we are talking about a *King Pin* in a beam axle arrangement, the KPI
angle is absolutely fixed and cannot be altered without recourse to
*bending* something.

What are you thinking of bending?

In terms of the beam axle arrangement, I can see nothing that I could
satisfactorily bend in order to correct a KPI angle but, for KPI to be
out, something has to have been *bent*.

In terms of modern cars, however, king pins are obsolete. The last
vehicle I can recall working on that had king pins was mid 60s.

What we use now are, as you know, ball joints to anchor the steering
knuckle yet allow multi-degree articulation. Makes the kinematics a damn
sight easier to work out from the engineer's design viewpoint.

https://www.freeasestudyguides.com/g...clination..png

In the diagram above, there is a line referencing *true vertical*,
another referencing the SAI *angle*, and another referencing the tyre
camber angle. The *included angle* cannot be altered. It is designed in
and the only way to change that would be to *bend something*. In this
case, that something would be the steering knuckle. Definitely not
recommended but something that used to be done in vehicles of the 50s
and 60s when you ran out of adjustment. I was fortunate I never needed
to do that.


I never bent a spindle, but the flamboprough hobby stock car guys did
sometimes. It was easier to use an AMC knuckle and just shim it - no
worrying about if you got the heat treat right -- - -

There was, IIRC, a limit to the number of degrees you could bend a
steering component *without* the application of heat. The application of
heat is always a worry because, if you get it wrong, well, **** happens.

Looking at the linked diagram, if I feel the camber angle is too great,
what options do I have. I have to move one of the ball joints in
relation to the other. Assume the adjustment for camber is shims at the
inner end of the top control arm. So I set to and remove sufficient
shims to move upper control arm, including the upper ball joint, inwards
and change the *camber angle*, say, 1 degree to the negative. That means
I have now *reduced* by 1 degree the angle between the true vertical and
centreline of the tyre. The tyre is now more vertical than it was.
But, if I cannot change the *included angle*. I must also have also
*increased* the angle between the true vertical and the *steering axis*
through the ball joints. That 1 degree of angle didn't just disappear,
it simply moved to the other side of that line that represents true
vertical. That means I have *increased* the steering axis *inclination*
from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
it will now be 10 degrees.

No - SAI IS the included angle.

Please, be informed that SAI is the angle through the steering axis
relative to the *true vertical*. The true vertical is the *vertical
reference*, an imaginary line drawn at right angles to the road surface.
It will always *remain* at right angles to the road surface regardless
of what is done to the SAI *angle* and/or the camber angle. The
*included angle*, by its very name, *includes* the SAI angle *and* the
camber angle. The included angle is designed in and cannot be changed by
normal means. The included angle is a diagnosis angle and, if deviated
from specifications, indicates that the steering knuckle has suffered
damage, ie bent steering knuckle.

You are right. It's been 36 years since I taught the stuff and 30
since I did it.

https://www.waybuilder.net/free-ed/S...s/09AdvW69.jpg

Do not be deceived by the angle at which the stub axle is drawn on the
above linked diagram. To be true to reality, the stub axle should have
been drawn at right angles to the blue centreline of the *wheel*. The
dotted blue line is not referencing anything on that diagram apart from
the horizontal datum line representing the road.

Camber IS the deviation from true vertical

We agree on one point at least. Yes, camber is the deviation from true
vertical. What we have, however, is a dispute regarding true vertical
and what it is referencing.

SAI is measured from the spindle centerline to the steering axis and

Correction, it not a reference to the spindle centreline, it is
referencing true vertical. The only point that doesn't change is the
true vertical since it is a vertical reference to the ground upon which
the vehicle is sitting and is at a *right angle* to it.

does NOT change, even if the car is laying on it's side. You get
CAMBER CHANGE with roll and squat - but you do NOT get SAI change.

If any steering axis *pivot* point moves laterally in relation to the
other pivot point, there will be a change in SAI relative to the true
vertical. There simply has to be. The included angle, since it is
*fixed* by design, cannot change. IOW, the angular relationship the
steering axis has with the camber angle is permanently fixed. The
included angle's relationship with the true vertical, however, is not fixed.



What can we see from this? The wheel will be more vertical, no doubt,
since we have reduced camber. But, because the steering axis inclination
has increased, we will likely experience heavier steering. That may or
may not be noticeable. The vehicle will have more steering self
centering.

How?

Any increase in SAI causes a commensurate increase in steering self
centering.

Take a good look at the Turnolgy site for some good explanations.

https://www.turnology.com/tech-stori...ke-you-faster/

We aren't looking at camber making a car faster. We are looking at
camber, under the influence of positive caster, making tyres wear on the
outside edge under severe steering lock situations at *low speed*.

YUes and no. He's not going down the hill fast - but if he went down
the hill much faster, he would not be staying on the road because he
is reaching the limit where the tire will just "let go" instead of
scuffing.

Also, we are likely to get more of a camber change on the
inner wheel when the steering turns to either lock. Remember, positive
caster is playing a role in this camber change too. Will it matter? I
can't say because I have always worked within manufacturers
specifications and I can't readily visualise the kinematics of it.

The one thing you will almost certainly have done is changed the slip
angles at the front wheels because that is what camber changes to the
negative at the front wheels do. That will have, in turn, altered the
oversteer/understeer balance between the front and rear of the vehicle.
Vehicles are given positive camber at the front wheels and zero or
negative camber at the rear. That promotes understeer, a safer situation
for the average driver. By reducing caster to the minimum spec, you will
achieve a similar outcome with regard to tyre wear but will not be
dicking with the handling balance.

When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is he
https://www.hotrod.com/articles/camb...tire-traction/.
It is slanted towards circle track racing, but covers all the basics.

Yes, but it covers all the basics with a distinct *bias*. For someone
who wants to learn about the basics, it is best they look at what is
done for *road going cars* first. It is a different world with regard to
handling. Sure, progress to racing cars but do get the basics down pat
first.

This IS a "handling" issue To be wearing the tires the way they are
being worn the vehicle is operating at the ragged edge of it's
handling capability on those carving downhills.

Um, no it is not. It is entirely *normal* given the nature of the
vehicle operation. Let me excerpt a snippet from an old text I used to
use when teaching this stuff;

I used to teach the stuff too. I used to do the alignments, and I
used to drive competitively
Caster Angle Tire Wear
The caster angle is generally considered to be a nontire wearing angle.
Although this statement is true, unequal or *excessive* caster can
*indirectly* cause tire wear. When the front wheels are turned on a
vehicle with a lot of positive caster, the front wheels become angled,
called camber *roll*.

Just look at a road grader

(The caster angle is a measurement of the
difference in camber angle from when the wheel is turned inward to when
the wheel is turned outward.) Many vehicle manufacturers have positive
caster designed into the suspension system. This positive caster has
increased the directional stability of these vehicles. However, if the
vehicle is used exclusively in city-type driving, the positive caster
can cause wear to the outside shoulders of both front tyres.
Automotive Chassis Systems, Brakes, Steering, Suspension and Alignment
James D. Halderman, 1996, Prentice Hall Inc.

I used Glenn's Automobile Engine Rebuilding and Maintenance,
Stockel's Auto Mechanic Fundamentals, and Crouse's Automotive
Mechanics. Also had a text on handling and suspension - can't remember
who wrote it or what it was called. It's LONG gone, it appears.

ANyway - from Modern Tire Dealer: Jan 2002 edition -

If the vehicle is normally, or routinely, driven under changing
lateral conditions (on curvy, twisty roads or on a road course), the
alignment angles will require a bias toward negative camber. When the
vehicle enters a turn, centrifugal force naturally moves the weight
mass toward the outside of the vehicle (if turning right, weight is
moved to the left; if turning left, mass momentum moves toward the
right). This causes the tires to flex both downward (pushing the tire
section toward the pavement) and laterally (to the outside, causing
the sidewall to allow the tire to lean).

If the static camber was set at zero, for example, a hard right turn
might cause the outside shoulder of the left front tire to bear the
brunt of the weight and scrubbing action, while a large percentage of
that tire´s center and inside tread area is lifted off the pavement.
The result: You´re only using a very tiny portion of the tread
(traction capability), while placing isolated wear on the outer
shoulder. This causes lousy handling in the turns and tires with
worn-out outer shoulders.

In order to compensate for this type of driving (lots of left/right
turns), we adjust the camber angle accordingly in order to benefit
from maximum tread contact in those turns. Once again, our goal is
simply to create a maximum tread contact patch under the vehicle´s
"typical" operating conditions.


Also see:

https://dsportmag.com/the-tech/extra...ment-settings/

See the section "effects of camber settings"

Also see:
https://www.youtube.com/watch?v=6Lnb7iQ1NJs

From Allpar - on alignment for early Mopars they have THIS to say:
Camber’s a whole different ball game. The factory never recommended
negative camber at all. (It’s negative when the top of the wheel tilts
in.) They had a good reason for this: they were trying to minimize
tire wear. With bias ply tires, camber is critical. Tilt the top in a
bit, and the inner edge of the skin will wear out—fast. With steel
belted radials, this is much less of a factor. Of course, there’s lots
of other factors at work he how stiff are the sidewalls? How much
air pressure do you run? How low is the aspect ratio (profile)? All of
these factors can affect the “best” (if there is such a thing) camber
number for you. If you have superlow- profile tires (like 40 series),
you might want a tad less camber. Ditto for high air pressures and/or
stiff sidewalls. You always (always) want at least a some negative
camber. Even with granny driving, there will be that emergency, kid
chasing a ball, etc., requiring an evasive maneuver. Having more
cornering G force at your disposal—via the more complete
tread/pavement contact afforded by the “preload” that negative camber
generates— is always a good thing.


The settings recommended and designed in to the vehicle are a
compromize - designed for acceptable handling and tire wear under
"normal" conditions. Same with tire pressures.

Under "abnormal" conditions - nose down, tight corners : you get both
squat and roll causing the camber to go positive - and you get weight
shift to the outside front corner, loading the outside front tire
significantly more than leveland straight driving - REQUIRING ahigher
tire pressure to "support" the load. It's the same as throwing 600
pounds into the trunk - only in reverse.


Regardless of the terminol;ogy (and I WAS wrong - and I admit it) the
SIMPLEST and MOST EFFECTIVE steps to reduce the tire wear a

#1 -check tire inflation and increase the front tire pressures -
basically to the spec for the rear tires fully loaded. - generally
about 5 to 10 PSI over the normal recommended tire pressure.
#2 - adjust the camber to 1 to 1.5 degrees more negative than spec if
possible.

This text is in full agreement with my diagnosis of Arlen's issue. His
issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
evidenced by the specific type of longitudinal feathering he is
experiencing on the outer shoulder of his tyres. It also supports the
partial solution that I offered, that he reduce his caster to the
minimum allowable specification. I have *known* of this issue for
*decades* but my current Toyota has given me my first personal
experience with it.

Not dissagreeing with your diagnosis

And I've dealt with it for years.About 90% of cars on the road are
running underinflated tires. PERHAPS just running the recommended
pressure may reduce the problem - IF the owner is allowing the
pressures to run too low - but a few extra PSI will NOT hurt - and
WILL help. I tend to drive a bit agressively - not as much as when
Iwas 50 years younger - and I ALWAYS run my front tires about 5 PSI
over spec - to prevent wearing the outer shoulders off my tires.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control

Sorry - I meant negative CAMBER

Negative caster is unusual on a RWD car since it has the nasty effect of
increasing body roll, highly undesirable. Negative caster is more usual
on a FWD because of drive torque as opposed to rolling resistance but it
is kept to a bare minimum. It would be interesting to see all the
steering geometry specifications for that vehicle.

arm suspension, and it handled like it was on rails . With the wide

I presume you mean SLA front suspension.
Yes - short and long arm

Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

That will depend entirely on the type of driving you do. If it's a lot
of highway driving, no problem. Light urban driving, again no problem.

Pretty agressive driving - - It had a 2300cc OHC engine with twin
CD175 Strombergs. I rallied it a couple times when the Renault wasn't
ready to go. I also chased it up and down Mount Washington and around
the Cabot Trail. I lent tit to my best man when his Lotus Cortina was
out of commission. Guys with Lotus Cortinas didn't generally baby
them.

The negative scrub radius helped tire wear and handling too, I
suspect. - - -
Our previous Toyota didn't show an issue but it was in an urban
environment most of its life. If you have lots of tight turns, as I have
experienced here and Arlen has experienced, you get camber scrub. It is
the compromise the manufacturers had to make given typical vehicle usage
patterns. Arlen's usage is not typical since he is doing lots of full
lock turns, grade notwithstanding. It is the full lock turns, with
attendant high positive camber gain on the inner wheel, that do the damage.

Along with the forward weight transfer and the centrifugal force
loading the outer tire. - and I agree - high positive camber gain -
not only from the tight lock, but also the squat and roll.

Vehicles with strut suspension require MORE negative static camber to
compensate effectively for cornering camber change




I will take your advice on the multi-side shoulder wear, by bringing the
front tires of this RWD vehicle to 40psi or so, which I understand and
where I appreciate that advice.

Since these tires were religiously rotated every 5K miles using a pattern I
devised myself of H-X-H-X-H-X, etc., the tires ended up wearing
"relatively" evenly overall, which is shown in this shot of the rears:
https://i.postimg.cc/63Kc80x9/mount29.jpg

I was just about to mount & balance these rear tires as we type where you
can see they're worn sort of kind of evenly except in the inside edge,
where these were mostly worn when on the front axle.

Just refresh my memory here, was it the *inside* or the *outside* of
your tread that was wearing more and with the longitudinal feathering?
Camber scrub tends to affect the *outside* edge of the tyre. For it to
affect the *inside edge*, the camber on the tyre would need to be going
well into the negative. It really can't be doing that. As I have stated
previously, the camber of the tyre on the outside of the turn loses
camber and goes more vertical whilst the tyre on the inside of the turn
goes from slightly positive to heavily positive. The tyre on the outside
of the turn could be heading slightly into negative territory but that
would depend on static camber settings and would be minimal. Certainly
the tyre at the high positive camber will be doing most of the shoulder
wearing in those sharp slow speed turns.

I likely should flip them on the wheel at the 10,000 mile mark after the
first two X-H rotations have been done, which will move the inside edge to
the outside edge. These darn tires have a whitewall stripe, which I hate,
so that's why I didn't flip them on the rims prior.

On Wed, 19 Jun 2019 04:50:08 -0000 (UTC), "Arlen G. Holder"
wrote:

On Wed, 19 Jun 2019 13:26:36 +1000, Xeno wrote:

We aren't looking at camber making a car faster. We are looking at
camber, under the influence of positive caster, making tyres wear on the
outside edge under severe steering lock situations at *low speed*.

Hi Xeno,
I agree with this special case, which most descriptions on the net ignore
since they're looking at racing versus nominally around 30mph.

Today I counted the steering wheel degrees, where on many turns it was only
90 degrees to the left and 90 degrees to the right, and on plenty others it
was 180 to the left or right, and on about 10% of the turns, it was more
than 360, where the biggest turns were more than 360 plus 90, and the less
biggest turns were slightly less than that, at about 375 degrees turning
the steering wheel.

I also hung a redneck lateral 'accelerometer' on the mirror, which was
simply the USB cable for the phone looped over the mirror, where it swung
from side to side constantly, but at about 45 degrees or less most of the
time. https://i.postimg.cc/L6CN5SKm/mount30.jpg

While it was hard to snap photos since one hand had to be on the steering
wheel, I had expected the loop of USB cable to swing further than 45
degrees but most of the time it seemed LESS than 45 degrees, I guess
because the speeds are so slow?
use a "g" meter app on your phone to check your lateral g-force.
Then check the deceleration G force going into the turn, and along
with the downhill slope, calculate the load on that outer front tire.
It WILL surprize you. Then check the required tire pressure for that
load - - - - - - - - - - - I'm guessing the load on that tire will be
approaching (or very possibly exceding) the static level load.

On 19/6/19 2:50 pm, Arlen G. Holder wrote:
On Wed, 19 Jun 2019 13:26:36 +1000, Xeno wrote:

We aren't looking at camber making a car faster. We are looking at
camber, under the influence of positive caster, making tyres wear on the
outside edge under severe steering lock situations at *low speed*.

Hi Xeno,
I agree with this special case, which most descriptions on the net ignore
since they're looking at racing versus nominally around 30mph.

Indeed, it is quite noticeable by its absence on the net. I suspect
that's because the number of people affected as much as you are is quite
minimal. I did once find a good description of it with pictures
describing the type of feathering but that seems to have vanished as has
a video that described exactly what happened during sharp cornering vis
a vis camber angles. I could have used a video like that in my teaching
days. That said, we had the teaching model that was used in the video, a
steering knuckle setup mounted on a bench, so I could have made the
video myself had I the time.

Today I counted the steering wheel degrees, where on many turns it was only
90 degrees to the left and 90 degrees to the right, and on plenty others it
was 180 to the left or right, and on about 10% of the turns, it was more
than 360, where the biggest turns were more than 360 plus 90, and the less
biggest turns were slightly less than that, at about 375 degrees turning
the steering wheel.

Yep, it's those full lock turns at low speed that does it. The vehicle
manufacturer has had to make a compromise here and you are at the wrong
end of his compromise.

I also hung a redneck lateral 'accelerometer' on the mirror, which was
simply the USB cable for the phone looped over the mirror, where it swung
from side to side constantly, but at about 45 degrees or less most of the
time. https://i.postimg.cc/L6CN5SKm/mount30.jpg

While it was hard to snap photos since one hand had to be on the steering
wheel, I had expected the loop of USB cable to swing further than 45
degrees but most of the time it seemed LESS than 45 degrees, I guess
because the speeds are so slow?



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On 19/6/19 2:51 pm, Clare Snyder wrote:
On Wed, 19 Jun 2019 13:26:36 +1000, Xeno
wrote:

On 19/6/19 4:27 am, Clare Snyder wrote:
On Wed, 19 Jun 2019 00:17:29 +1000, Xeno
wrote:

On 18/6/19 12:58 am, Clare Snyder wrote:
On Mon, 17 Jun 2019 15:01:47 +1000, Xeno
wrote:

On 17/6/19 8:48 am, Arlen G. Holder wrote:
On Sun, 16 Jun 2019 17:39:04 -0400, Clare Snyder wrote:

Just applying negative camber MAY be simpler and will accomplish the
same thing, without affecting lateral stability..

However, with the shoulder wear on BOTH edges, the most effective
change you can make is to "air up" the tires. Keep the carcass of the
tire rigid - prevent the tire from "rolling" out on the outer corner
and "rolling in" on the inner corner will cause the tread to wear more
evenly across the face of the tire - and tereby REDUCE the total wear.
I'd bet about 3/4 of the wear is caused on the downhill.

Hi Clare,
I appreciate your advice as you and Xeno know this stuff whereas the rest
just make it all up it seems.

If adding more negative camber is even better than reducing the positive
caster, then that's easier, as you noted, and likely better on high speed
straight-line driving (we don't do high speed cornering ever).

Adding more negative camber also increases SAI, one follows the other
and SAI is not separately adjustable since it is designed in. That means
your negative camber increase will increase SAI. As I have previously
stated, steering and suspension geometry is one huge compromise so you
need to think carefully about the unintended consequences of *any* non
standard setting you use. That's why I said to ensure your caster spec
was on the *low side* of the acceptable range. That will ensure the
least amount of unintended consequences as it will still be within
factory spec.


Adding negative camber will countderact the effects of SAI. Increased
SAI (or "included angle" in the spindle) causes more change in camber
as the wheel leaves the center position.. Changing camber DOES NOT
AFFECT SAI.

Are you sure about that? SAI is, after all, Steering Axis Inclination.


100%
KPI or SAI is also known as the "included angle" and is the angle
between the centerline of the steering axis and the centerline of the
wheel axis (or spindle) Without bending the pdindle assembly it
cannot be changed on modern vehicles. On older AMC and a few others
with bolt-on spindles (including SOME current FWD vehicles you CAN
change the SAI somewhat by inserting tapered shims between the knuckle
and the spindle. MOST RWD cars and a large number of FWD today do NOT
use a bolt-on spindle or a bolt-on bearing housing, making it
impossible. On the 2 part knuckles (separate knuckle and spindle) we
used to occaisionally shim them for" competition"

If we are talking about a *King Pin* in a beam axle arrangement, the KPI
angle is absolutely fixed and cannot be altered without recourse to
*bending* something.

What are you thinking of bending?

In terms of the beam axle arrangement, I can see nothing that I could
satisfactorily bend in order to correct a KPI angle but, for KPI to be
out, something has to have been *bent*.

In terms of modern cars, however, king pins are obsolete. The last
vehicle I can recall working on that had king pins was mid 60s.

What we use now are, as you know, ball joints to anchor the steering
knuckle yet allow multi-degree articulation. Makes the kinematics a damn
sight easier to work out from the engineer's design viewpoint.

https://www.freeasestudyguides.com/g...clination..png

In the diagram above, there is a line referencing *true vertical*,
another referencing the SAI *angle*, and another referencing the tyre
camber angle. The *included angle* cannot be altered. It is designed in
and the only way to change that would be to *bend something*. In this
case, that something would be the steering knuckle. Definitely not
recommended but something that used to be done in vehicles of the 50s
and 60s when you ran out of adjustment. I was fortunate I never needed
to do that.


I never bent a spindle, but the flamboprough hobby stock car guys did
sometimes. It was easier to use an AMC knuckle and just shim it - no
worrying about if you got the heat treat right -- - -

There was, IIRC, a limit to the number of degrees you could bend a
steering component *without* the application of heat. The application of
heat is always a worry because, if you get it wrong, well, **** happens.

Looking at the linked diagram, if I feel the camber angle is too great,
what options do I have. I have to move one of the ball joints in
relation to the other. Assume the adjustment for camber is shims at the
inner end of the top control arm. So I set to and remove sufficient
shims to move upper control arm, including the upper ball joint, inwards
and change the *camber angle*, say, 1 degree to the negative. That means
I have now *reduced* by 1 degree the angle between the true vertical and
centreline of the tyre. The tyre is now more vertical than it was.
But, if I cannot change the *included angle*. I must also have also
*increased* the angle between the true vertical and the *steering axis*
through the ball joints. That 1 degree of angle didn't just disappear,
it simply moved to the other side of that line that represents true
vertical. That means I have *increased* the steering axis *inclination*
from the true vertical by 1 degree. If SAI was, say, 9 degrees before,
it will now be 10 degrees.

No - SAI IS the included angle.

Please, be informed that SAI is the angle through the steering axis
relative to the *true vertical*. The true vertical is the *vertical
reference*, an imaginary line drawn at right angles to the road surface.
It will always *remain* at right angles to the road surface regardless
of what is done to the SAI *angle* and/or the camber angle. The
*included angle*, by its very name, *includes* the SAI angle *and* the
camber angle. The included angle is designed in and cannot be changed by
normal means. The included angle is a diagnosis angle and, if deviated
from specifications, indicates that the steering knuckle has suffered
damage, ie bent steering knuckle.

You are right. It's been 36 years since I taught the stuff and 30
since I did it.

In my case, 18 years since I both taught and did it. 18 years also since
I last had access to the latest version of a computerised 4 wheel
aligner and a full steering, suspension and brake shop. I really miss
that access.

https://www.waybuilder.net/free-ed/S...s/09AdvW69.jpg

Do not be deceived by the angle at which the stub axle is drawn on the
above linked diagram. To be true to reality, the stub axle should have
been drawn at right angles to the blue centreline of the *wheel*. The
dotted blue line is not referencing anything on that diagram apart from
the horizontal datum line representing the road.

Camber IS the deviation from true vertical

We agree on one point at least. Yes, camber is the deviation from true
vertical. What we have, however, is a dispute regarding true vertical
and what it is referencing.

SAI is measured from the spindle centerline to the steering axis and

Correction, it not a reference to the spindle centreline, it is
referencing true vertical. The only point that doesn't change is the
true vertical since it is a vertical reference to the ground upon which
the vehicle is sitting and is at a *right angle* to it.

does NOT change, even if the car is laying on it's side. You get
CAMBER CHANGE with roll and squat - but you do NOT get SAI change.

If any steering axis *pivot* point moves laterally in relation to the
other pivot point, there will be a change in SAI relative to the true
vertical. There simply has to be. The included angle, since it is
*fixed* by design, cannot change. IOW, the angular relationship the
steering axis has with the camber angle is permanently fixed. The
included angle's relationship with the true vertical, however, is not fixed.



What can we see from this? The wheel will be more vertical, no doubt,
since we have reduced camber. But, because the steering axis inclination
has increased, we will likely experience heavier steering. That may or
may not be noticeable. The vehicle will have more steering self
centering.

How?

Any increase in SAI causes a commensurate increase in steering self
centering.

Take a good look at the Turnolgy site for some good explanations.

https://www.turnology.com/tech-stori...ke-you-faster/

We aren't looking at camber making a car faster. We are looking at
camber, under the influence of positive caster, making tyres wear on the
outside edge under severe steering lock situations at *low speed*.

YUes and no. He's not going down the hill fast - but if he went down
the hill much faster, he would not be staying on the road because he
is reaching the limit where the tire will just "let go" instead of
scuffing.

What you need to keep in mind here is that, with a decent amount of
positive caster, the wheel on the outside of the bend goes more vertical
due to camber roll, the opposite of what the wheel on the inside of the
bend is doing. It is, in effect, losing camber so it will not be riding
hard on the edges of its tyres. That is what it needs to do to maintain
a full tyre contact patch and resist the G Forces in the turn. The inner
tyre isn't so fortunate, it gains heaps of positive camber, loses the
contact patch on the inner edges of the tread and scuffs much more.


Also, we are likely to get more of a camber change on the
inner wheel when the steering turns to either lock. Remember, positive
caster is playing a role in this camber change too. Will it matter? I
can't say because I have always worked within manufacturers
specifications and I can't readily visualise the kinematics of it.

The one thing you will almost certainly have done is changed the slip
angles at the front wheels because that is what camber changes to the
negative at the front wheels do. That will have, in turn, altered the
oversteer/understeer balance between the front and rear of the vehicle.
Vehicles are given positive camber at the front wheels and zero or
negative camber at the rear. That promotes understeer, a safer situation
for the average driver. By reducing caster to the minimum spec, you will
achieve a similar outcome with regard to tyre wear but will not be
dicking with the handling balance.

When turning in a downhill thrusting turn the outer tire
will have a negative shift in camber while the inner wheel will have a
positive shift. The more positive caster, the more pronounced this
"tilt" or "corner carving" tendancy. If the tires are not stiff
enough or are underinflated, the tires will wear excessively on the
side facing the outside of the turn. If the tires ARE stiff enough or
inflated hard, the wear will tend to move towards the side of the tire
on the INSIDE of the turn - tending to even the wear across the face
of the tire.

That's why my FIRST recommendation is to air up the tires, and to
reduce the wear on the outside of the turn, possibly increase the
negative camber. Setting the caster to the high side of the positive
spec will give you extra negative camber on turns without any possible
negative effects of negative camber on the straight and level. It's
all a compromize. Dive and roll come into play along with road
banking.

a good article on camber change is he
https://www.hotrod.com/articles/camb...tire-traction/.
It is slanted towards circle track racing, but covers all the basics.

Yes, but it covers all the basics with a distinct *bias*. For someone
who wants to learn about the basics, it is best they look at what is
done for *road going cars* first. It is a different world with regard to
handling. Sure, progress to racing cars but do get the basics down pat
first.

This IS a "handling" issue To be wearing the tires the way they are
being worn the vehicle is operating at the ragged edge of it's
handling capability on those carving downhills.

Um, no it is not. It is entirely *normal* given the nature of the
vehicle operation. Let me excerpt a snippet from an old text I used to
use when teaching this stuff;

I used to teach the stuff too. I used to do the alignments, and I
used to drive competitively

I wasn't a competition driver. I was a pit crew member in a stock car
racing team at one time. That was over 40 years ago when I was young and
single.

Caster Angle Tire Wear
The caster angle is generally considered to be a nontire wearing angle.
Although this statement is true, unequal or *excessive* caster can
*indirectly* cause tire wear. When the front wheels are turned on a
vehicle with a lot of positive caster, the front wheels become angled,
called camber *roll*.

Just look at a road grader

A road grader is a different kettle of fish. Their steering is much more
flexible in its control than the average car. It needs to be in order to
provide a bias against the action of the blade. For instance, they can
*tilt* both steering wheels in the same direction.

(The caster angle is a measurement of the
difference in camber angle from when the wheel is turned inward to when
the wheel is turned outward.) Many vehicle manufacturers have positive
caster designed into the suspension system. This positive caster has
increased the directional stability of these vehicles. However, if the
vehicle is used exclusively in city-type driving, the positive caster
can cause wear to the outside shoulders of both front tyres.
Automotive Chassis Systems, Brakes, Steering, Suspension and Alignment
James D. Halderman, 1996, Prentice Hall Inc.

I used Glenn's Automobile Engine Rebuilding and Maintenance,
Stockel's Auto Mechanic Fundamentals, and Crouse's Automotive
Mechanics. Also had a text on handling and suspension - can't remember
who wrote it or what it was called. It's LONG gone, it appears.

I used Stockel when I was an apprentice. That was a very long time ago
and it was very good on the fundamentals. At the college we used an
Aussie version of Crouse's text, in collaboration with Ed May. Still
have the 2 volume 5th edition that was current when I retired from
teaching. I recently gave away the much earlier edition I had to a
friend who restores the kinds of cars covered by that book. As for
engine rebuilding, the go to reference in this country was the Repco
Engine Manual. I had two copies of that, gave the older version away to
the same friend mentioned above.
I still have quite a few books on suspensions, steering & handling;
Chassis Engineering, Herb Adams
The Race Car Chassis, Forbes Aird
How To Make Your Car Handle, Fred Puhn
Racing Car Design & Development, Len Terry, Alan Baker
Chassis Tuning, Jan P Norbye
Design Of racing Sports Cars, Colin Campbell
Automobile Suspensions, Colin Campbell
New Directions In Suspension Design, Colin Campbell
The Sports Car - Its Design and Performance, Colin Campbell
Car Suspension At Work, Jeffrey Daniels
Competition Car Suspension, Allan Staniforth

I have several more but the above are the ones more focused on the
performance and handling side of vehicles rather than the fundamental
principles. Most are getting rather long in the tooth now and don't
adequately reflect current trends.


ANyway - from Modern Tire Dealer: Jan 2002 edition -

If the vehicle is normally, or routinely, driven under changing
lateral conditions (on curvy, twisty roads or on a road course), the
alignment angles will require a bias toward negative camber. When the
vehicle enters a turn, centrifugal force naturally moves the weight
mass toward the outside of the vehicle (if turning right, weight is
moved to the left; if turning left, mass momentum moves toward the
right). This causes the tires to flex both downward (pushing the tire
section toward the pavement) and laterally (to the outside, causing
the sidewall to allow the tire to lean).

If the static camber was set at zero, for example, a hard right turn
might cause the outside shoulder of the left front tire to bear the
brunt of the weight and scrubbing action, while a large percentage of
that tire´s center and inside tread area is lifted off the pavement.
The result: You´re only using a very tiny portion of the tread
(traction capability), while placing isolated wear on the outer
shoulder. This causes lousy handling in the turns and tires with
worn-out outer shoulders.

I have no issue with that but the type of feathered edge on Arlen's
vehicle indicated to me that it wasn't a pure camber issue.

In order to compensate for this type of driving (lots of left/right
turns), we adjust the camber angle accordingly in order to benefit
from maximum tread contact in those turns. Once again, our goal is
simply to create a maximum tread contact patch under the vehicle´s
"typical" operating conditions.


Also see:

https://dsportmag.com/the-tech/extra...ment-settings/

See the section "effects of camber settings"

Also see:
https://www.youtube.com/watch?v=6Lnb7iQ1NJs

From Allpar - on alignment for early Mopars they have THIS to say:
Cambers a whole different ball game. The factory never recommended
negative camber at all. (Its negative when the top of the wheel tilts
in.) They had a good reason for this: they were trying to minimize
tire wear. With bias ply tires, camber is critical. Tilt the top in a
bit, and the inner edge of the skin will wear out€”fast. With steel
belted radials, this is much less of a factor. Of course, theres lots
of other factors at work he how stiff are the sidewalls? How much
air pressure do you run? How low is the aspect ratio (profile)? All of
these factors can affect the €œbest€� (if there is such a thing) camber
number for you. If you have superlow- profile tires (like 40 series),
you might want a tad less camber. Ditto for high air pressures and/or
stiff sidewalls. You always (always) want at least a some negative
camber. Even with granny driving, there will be that emergency, kid
chasing a ball, etc., requiring an evasive maneuver. Having more
cornering G force at your disposal€”via the more complete
tread/pavement contact afforded by the €œpreload€� that negative camber
generates€” is always a good thing.

What they don't say is that negative camber will decrease the slip angle
at the front wheels whilst leaving the rear as standard. That will lead
to a snap oversteering car and *granny* may find that more than a little
disconcerting.

The settings recommended and designed in to the vehicle are a
compromize - designed for acceptable handling and tire wear under
"normal" conditions. Same with tire pressures.

Always. You can change the understeer/oversteer balance with tyre
pressures alone.

Under "abnormal" conditions - nose down, tight corners : you get both
squat and roll causing the camber to go positive - and you get weight
shift to the outside front corner, loading the outside front tire
significantly more than leveland straight driving - REQUIRING ahigher
tire pressure to "support" the load. It's the same as throwing 600
pounds into the trunk - only in reverse.


Regardless of the terminol;ogy (and I WAS wrong - and I admit it) the
SIMPLEST and MOST EFFECTIVE steps to reduce the tire wear a

#1 -check tire inflation and increase the front tire pressures -
basically to the spec for the rear tires fully loaded. - generally
about 5 to 10 PSI over the normal recommended tire pressure.
#2 - adjust the camber to 1 to 1.5 degrees more negative than spec if
possible.

This text is in full agreement with my diagnosis of Arlen's issue. His
issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
evidenced by the specific type of longitudinal feathering he is
experiencing on the outer shoulder of his tyres. It also supports the
partial solution that I offered, that he reduce his caster to the
minimum allowable specification. I have *known* of this issue for
*decades* but my current Toyota has given me my first personal
experience with it.

Not dissagreeing with your diagnosis

Thanks for that.

And I've dealt with it for years.About 90% of cars on the road are
running underinflated tires. PERHAPS just running the recommended
pressure may reduce the problem - IF the owner is allowing the
pressures to run too low - but a few extra PSI will NOT hurt - and
WILL help. I tend to drive a bit agressively - not as much as when
Iwas 50 years younger - and I ALWAYS run my front tires about 5 PSI
over spec - to prevent wearing the outer shoulders off my tires.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control

Sorry - I meant negative CAMBER

Ah, that explains it then.

Negative caster is unusual on a RWD car since it has the nasty effect of
increasing body roll, highly undesirable. Negative caster is more usual
on a FWD because of drive torque as opposed to rolling resistance but it
is kept to a bare minimum. It would be interesting to see all the
steering geometry specifications for that vehicle.

arm suspension, and it handled like it was on rails . With the wide

I presume you mean SLA front suspension.
Yes - short and long arm

Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

That will depend entirely on the type of driving you do. If it's a lot
of highway driving, no problem. Light urban driving, again no problem.

Pretty agressive driving - - It had a 2300cc OHC engine with twin
CD175 Strombergs. I rallied it a couple times when the Renault wasn't
ready to go. I also chased it up and down Mount Washington and around
the Cabot Trail. I lent tit to my best man when his Lotus Cortina was
out of commission. Guys with Lotus Cortinas didn't generally baby
them.

The Vauxhall Firenza never made it to these shores. I see it had a very
brief life - 3 years.

The negative scrub radius helped tire wear and handling too, I
suspect. - - -

Definitely a safer way to go!

Our previous Toyota didn't show an issue but it was in an urban
environment most of its life. If you have lots of tight turns, as I have
experienced here and Arlen has experienced, you get camber scrub. It is
the compromise the manufacturers had to make given typical vehicle usage
patterns. Arlen's usage is not typical since he is doing lots of full
lock turns, grade notwithstanding. It is the full lock turns, with
attendant high positive camber gain on the inner wheel, that do the damage.

Along with the forward weight transfer and the centrifugal force
loading the outer tire. - and I agree - high positive camber gain -
not only from the tight lock, but also the squat and roll.

Most suspensions systems have a fair degree of anti-dive geometry built
into them these days so it's not the problem it was. Positive caster
jacks up the outer wheel so that should counter it as well.

Suspension systems, the SLA in particular, allow (cause) the front
camber to change under deflection. With an SLA front suspension at
normal ride height, the camber is at its static setting. Assume its
static setting is 0, neither negative or positive. As the wheel is
deflected up over a bump, the short arm will track a smaller radius than
the longer lower arm. This means the upper ball joint will be pulled
inwards at a greater rate than the lower ball joint. Because of this,
the camber actually goes more negative as the suspension is deflected
upwards. The benefit of this is that track width doesn't change under
single or two wheel deflection since the tyre at the contact patch
maintains its fore and aft alignment. Under body roll in a turn, the
inner mount of the upper arm may track outwards. This would normally
cause a camber change to the positive but, because of the short arm's
negative effect on camber change, the effect of each cancels the other
out and camber remains at or close to the static setting. IOW, the wheel
remains close to vertical and the contact patch and slip angles are
minimally affected. This is one of the reasons the racing fraternity
prefer SLA suspensions in either 4 link or 5 link varieties.

https://www.imperial.ac.uk/news/imag...2012/21320.jpg

Note too that the action depicted above by the SLA suspension is in
straight ahead situations. It does not take into account any camber roll
that occurs when the wheel is in a tight turn which, if the outside
wheel is already at a neutral camber, will cause it to become decidedly
negative.

One thing I have learnt about steering and suspensions over the years,
the more you learn, the more you realise you don't know.

--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On Wed, 19 Jun 2019 21:48:30 +1000, Xeno
wrote:

On 19/6/19 2:51 pm, Clare Snyder wrote:
On Wed, 19 Jun 2019 13:26:36 +1000, Xeno
wrote:

On 19/6/19 4:27 am, Clare Snyder wrote:
On Wed, 19 Jun 2019 00:17:29 +1000, Xeno
wrote:

I have several more but the above are the ones more focused on the
performance and handling side of vehicles rather than the fundamental
principles. Most are getting rather long in the tooth now and don't
adequately reflect current trends.

If I had a need to "design" a suspension system I'd just ask my
good friend Gary who has forgotten more than I ever knew about
performance suspension and chassis. When it comes to figuring out
what's wrong with an existing vehicle for a given application I've had
a pretty good record at sorting it out.

ANyway - from Modern Tire Dealer: Jan 2002 edition -

If the vehicle is normally, or routinely, driven under changing
lateral conditions (on curvy, twisty roads or on a road course), the
alignment angles will require a bias toward negative camber. When the
vehicle enters a turn, centrifugal force naturally moves the weight
mass toward the outside of the vehicle (if turning right, weight is
moved to the left; if turning left, mass momentum moves toward the
right). This causes the tires to flex both downward (pushing the tire
section toward the pavement) and laterally (to the outside, causing
the sidewall to allow the tire to lean).

If the static camber was set at zero, for example, a hard right turn
might cause the outside shoulder of the left front tire to bear the
brunt of the weight and scrubbing action, while a large percentage of
that tire´s center and inside tread area is lifted off the pavement.
The result: You´re only using a very tiny portion of the tread
(traction capability), while placing isolated wear on the outer
shoulder. This causes lousy handling in the turns and tires with
worn-out outer shoulders.

I have no issue with that but the type of feathered edge on Arlen's
vehicle indicated to me that it wasn't a pure camber issue.

Is there ever a "pure" anything issue???

In order to compensate for this type of driving (lots of left/right
turns), we adjust the camber angle accordingly in order to benefit
from maximum tread contact in those turns. Once again, our goal is
simply to create a maximum tread contact patch under the vehicle´s
"typical" operating conditions.


Also see:

https://dsportmag.com/the-tech/extra...ment-settings/

See the section "effects of camber settings"

Also see:
https://www.youtube.com/watch?v=6Lnb7iQ1NJs

From Allpar - on alignment for early Mopars they have THIS to say:
Camber’s a whole different ball game. The factory never recommended
negative camber at all. (It’s negative when the top of the wheel tilts
in.) They had a good reason for this: they were trying to minimize
tire wear. With bias ply tires, camber is critical. Tilt the top in a
bit, and the inner edge of the skin will wear out—fast. With steel
belted radials, this is much less of a factor. Of course, there’s lots
of other factors at work he how stiff are the sidewalls? How much
air pressure do you run? How low is the aspect ratio (profile)? All of
these factors can affect the “best” (if there is such a thing) camber
number for you. If you have superlow- profile tires (like 40 series),
you might want a tad less camber. Ditto for high air pressures and/or
stiff sidewalls. You always (always) want at least a some negative
camber. Even with granny driving, there will be that emergency, kid
chasing a ball, etc., requiring an evasive maneuver. Having more
cornering G force at your disposal—via the more complete
tread/pavement contact afforded by the “preload” that negative camber
generates— is always a good thing.

What they don't say is that negative camber will decrease the slip angle
at the front wheels whilst leaving the rear as standard. That will lead
to a snap oversteering car and *granny* may find that more than a little
disconcerting.


You are worried about "snap oversteer" at under 30 MPH - - - -
The settings recommended and designed in to the vehicle are a
compromize - designed for acceptable handling and tire wear under
"normal" conditions. Same with tire pressures.

Always. You can change the understeer/oversteer balance with tyre
pressures alone.

Which is why I recommended tire pressure check FIRST.

Under "abnormal" conditions - nose down, tight corners : you get both
squat and roll causing the camber to go positive - and you get weight
shift to the outside front corner, loading the outside front tire
significantly more than leveland straight driving - REQUIRING ahigher
tire pressure to "support" the load. It's the same as throwing 600
pounds into the trunk - only in reverse.


Regardless of the terminol;ogy (and I WAS wrong - and I admit it) the
SIMPLEST and MOST EFFECTIVE steps to reduce the tire wear a

#1 -check tire inflation and increase the front tire pressures -
basically to the spec for the rear tires fully loaded. - generally
about 5 to 10 PSI over the normal recommended tire pressure.
#2 - adjust the camber to 1 to 1.5 degrees more negative than spec if
possible.

This text is in full agreement with my diagnosis of Arlen's issue. His
issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
evidenced by the specific type of longitudinal feathering he is
experiencing on the outer shoulder of his tyres. It also supports the
partial solution that I offered, that he reduce his caster to the
minimum allowable specification. I have *known* of this issue for
*decades* but my current Toyota has given me my first personal
experience with it.

Not dissagreeing with your diagnosis

Thanks for that.

And I've dealt with it for years.About 90% of cars on the road are
running underinflated tires. PERHAPS just running the recommended
pressure may reduce the problem - IF the owner is allowing the
pressures to run too low - but a few extra PSI will NOT hurt - and
WILL help. I tend to drive a bit agressively - not as much as when
Iwas 50 years younger - and I ALWAYS run my front tires about 5 PSI
over spec - to prevent wearing the outer shoulders off my tires.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control

Sorry - I meant negative CAMBER

Ah, that explains it then.

Negative caster is unusual on a RWD car since it has the nasty effect of
increasing body roll, highly undesirable. Negative caster is more usual
on a FWD because of drive torque as opposed to rolling resistance but it
is kept to a bare minimum. It would be interesting to see all the
steering geometry specifications for that vehicle.

arm suspension, and it handled like it was on rails . With the wide

I presume you mean SLA front suspension.
Yes - short and long arm

Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

That will depend entirely on the type of driving you do. If it's a lot
of highway driving, no problem. Light urban driving, again no problem.

Pretty agressive driving - - It had a 2300cc OHC engine with twin
CD175 Strombergs. I rallied it a couple times when the Renault wasn't
ready to go. I also chased it up and down Mount Washington and around
the Cabot Trail. I lent tit to my best man when his Lotus Cortina was
out of commission. Guys with Lotus Cortinas didn't generally baby
them.

The Vauxhall Firenza never made it to these shores. I see it had a very
brief life - 3 years.

The USA got the Opel - we got the Vauxhall. Whether sold as a Viva HC
or a Firenza it was the same car. Also sold as the Magnum in the UK

The negative scrub radius helped tire wear and handling too, I
suspect. - - -

Definitely a safer way to go!

Our previous Toyota didn't show an issue but it was in an urban
environment most of its life. If you have lots of tight turns, as I have
experienced here and Arlen has experienced, you get camber scrub. It is
the compromise the manufacturers had to make given typical vehicle usage
patterns. Arlen's usage is not typical since he is doing lots of full
lock turns, grade notwithstanding. It is the full lock turns, with
attendant high positive camber gain on the inner wheel, that do the damage.

Along with the forward weight transfer and the centrifugal force
loading the outer tire. - and I agree - high positive camber gain -
not only from the tight lock, but also the squat and roll.

Most suspensions systems have a fair degree of anti-dive geometry built
into them these days so it's not the problem it was. Positive caster
jacks up the outer wheel so that should counter it as well.

Suspension systems, the SLA in particular, allow (cause) the front
camber to change under deflection. With an SLA front suspension at
normal ride height, the camber is at its static setting. Assume its
static setting is 0, neither negative or positive. As the wheel is
deflected up over a bump, the short arm will track a smaller radius than
the longer lower arm. This means the upper ball joint will be pulled
inwards at a greater rate than the lower ball joint. Because of this,
the camber actually goes more negative as the suspension is deflected
upwards. The benefit of this is that track width doesn't change under
single or two wheel deflection since the tyre at the contact patch
maintains its fore and aft alignment. Under body roll in a turn, the
inner mount of the upper arm may track outwards. This would normally
cause a camber change to the positive but, because of the short arm's
negative effect on camber change, the effect of each cancels the other
out and camber remains at or close to the static setting. IOW, the wheel
remains close to vertical and the contact patch and slip angles are
minimally affected. This is one of the reasons the racing fraternity
prefer SLA suspensions in either 4 link or 5 link varieties.

And the sla suspension is designed to do what I am recommending to do
- but just not enough for THIS situation. By starting with a static
negative you are just helping the factory design do a better job.

https://www.imperial.ac.uk/news/imag...2012/21320.jpg

Note too that the action depicted above by the SLA suspension is in
straight ahead situations. It does not take into account any camber roll
that occurs when the wheel is in a tight turn which, if the outside
wheel is already at a neutral camber, will cause it to become decidedly
negative.


Which is what you want - and adding an extra 1.5 degrees or so can
only help
One thing I have learnt about steering and suspensions over the years,
the more you learn, the more you realise you don't know.


"If I knew then what I know now I wouldn't know what I know now"

On 20/6/19 7:42 am, Clare Snyder wrote:
On Wed, 19 Jun 2019 21:48:30 +1000, Xeno
wrote:

On 19/6/19 2:51 pm, Clare Snyder wrote:
On Wed, 19 Jun 2019 13:26:36 +1000, Xeno
wrote:

On 19/6/19 4:27 am, Clare Snyder wrote:
On Wed, 19 Jun 2019 00:17:29 +1000, Xeno
wrote:

I have several more but the above are the ones more focused on the
performance and handling side of vehicles rather than the fundamental
principles. Most are getting rather long in the tooth now and don't
adequately reflect current trends.

If I had a need to "design" a suspension system I'd just ask my
good friend Gary who has forgotten more than I ever knew about
performance suspension and chassis. When it comes to figuring out
what's wrong with an existing vehicle for a given application I've had
a pretty good record at sorting it out.

My point in referring to those books on performance chassis and
suspension systems is that it gives you insight into why things are
designed in the way they are on *road going cars* by comparing them to
what the racers do. The design decisions are way different, not only
because the environment is different but also because the race drivers
are much more attuned to the handling of their cars. What is more, those
drivers will know how to tweak their car's handling to suit their own
personal preference.

When the designers get it wrong, they do it spectacularly. The A Class
Benz, when it was first released, was just such a cockup. In the Moose
Test, it *fell over*. The natural roll resonance frequency of the rear
suspension in the A Class near enough coincided with the 4 yaw reversals
in the Elk Test so that each directional change *added* further to the
toppling force until it became large enough to tip the car beyond the
fulcrum of its outer tyre contact patches. It takes very precise
counter-steering to correct such a thing *in real time* and the Benz
solution was a number of modifications. The first was to modify the
suspension by uprating spring and damper frequencies which increased the
natural rolling frequency. That reduced the yaw enhancement coincidence
effect but, because of extremes of loading between empty and full,
didn't entirely remove it under all circumstances. Remember, the A Class
did the Elk Test with a *full load*. The rear track was widened, this
then required a greater side force to tip the car over. A stiffer front
anti-roll bar was fitted which increased understeer but also reduced the
tendency to tail swing in lane changing manoeuvres. This increased front
tyre slip angles and rolling resistance thus causing the car to slow
more quickly. The tyres were standardised at 195/50-15 instead of the
original 175/65-15. These had a 10mm smaller rolling diameter lowering
both the roll centre and CofG but also, to the negative, increased
slightly the critical overturning moment. There were most likely other
kinematic changes made to the front and rear suspensions and, though I
can take an educated guess as to where these might have been made, I
have seen no further detail concerning them. As a finale, stability
control was fitted *as standard*, which Benz call ESP, and the precise
braking reactions that the ESP gave, which in turn provided precise
counter steering, finally solved the issue.

https://www.carsifu.my/news/cars-are...amous-elk-test

In the hands of a racing car driver, the A class, in its original form,
would likely not have rolled on the Moose Test. The target market
however was not racing car drivers. In the hands of an average driver,
the A Class was potentially lethal. The primary error was in the natural
roll resonance frequency. All the Benz engineers were trying to do was
improve the ride quality but, in doing so, created an unintended
consequence. What was worse though was that the issue was not discovered
in testing. Obviously their testing regime was insufficiently broad.

I was trained as a mechanic, not a design engineer, so I could quite
easily have modified a car with different springs and created such a
scenario as befell the A Class.
This book; https://www.sae.org/publications/books/content/r-114/
was one I purchased a very long time ago soon after it was published.
This and others subsequently enabled me to gain the insight that I
needed in order to alert apprentices of the unintended consequences of
their car modifications by better understanding vehicle dynamics. A
simple example is the lowering of a car by use of shorter coils. It
upsets the kinematics of the suspension and you get unintended
consequences such as described in this video clip.
https://www.whiteline.com.au/roll_centre_kits.php
When I was teaching apprentices, the internet was not the vast resource
that it is today and their reference material did not extend to such
esoteric areas as vehicle dynamics. Even now, if you scan though
training texts for mechanics, you find information on steering and
suspensions sparse beyond the basics needed to service and repair them.



ANyway - from Modern Tire Dealer: Jan 2002 edition -

If the vehicle is normally, or routinely, driven under changing
lateral conditions (on curvy, twisty roads or on a road course), the
alignment angles will require a bias toward negative camber. When the
vehicle enters a turn, centrifugal force naturally moves the weight
mass toward the outside of the vehicle (if turning right, weight is
moved to the left; if turning left, mass momentum moves toward the
right). This causes the tires to flex both downward (pushing the tire
section toward the pavement) and laterally (to the outside, causing
the sidewall to allow the tire to lean).

If the static camber was set at zero, for example, a hard right turn
might cause the outside shoulder of the left front tire to bear the
brunt of the weight and scrubbing action, while a large percentage of
that tire´s center and inside tread area is lifted off the pavement.
The result: You´re only using a very tiny portion of the tread
(traction capability), while placing isolated wear on the outer
shoulder. This causes lousy handling in the turns and tires with
worn-out outer shoulders.

I have no issue with that but the type of feathered edge on Arlen's
vehicle indicated to me that it wasn't a pure camber issue.

Is there ever a "pure" anything issue???

No but, as stated, that particular feathered tread effect was pretty
unequivocal as to its cause.

In order to compensate for this type of driving (lots of left/right
turns), we adjust the camber angle accordingly in order to benefit
from maximum tread contact in those turns. Once again, our goal is
simply to create a maximum tread contact patch under the vehicle´s
"typical" operating conditions.


Also see:

https://dsportmag.com/the-tech/extra...ment-settings/

See the section "effects of camber settings"

Also see:
https://www.youtube.com/watch?v=6Lnb7iQ1NJs

From Allpar - on alignment for early Mopars they have THIS to say:
Cambers a whole different ball game. The factory never recommended
negative camber at all. (Its negative when the top of the wheel tilts
in.) They had a good reason for this: they were trying to minimize
tire wear. With bias ply tires, camber is critical. Tilt the top in a
bit, and the inner edge of the skin will wear out€”fast. With steel
belted radials, this is much less of a factor. Of course, theres lots
of other factors at work he how stiff are the sidewalls? How much
air pressure do you run? How low is the aspect ratio (profile)? All of
these factors can affect the €œbest€� (if there is such a thing) camber
number for you. If you have superlow- profile tires (like 40 series),
you might want a tad less camber. Ditto for high air pressures and/or
stiff sidewalls. You always (always) want at least a some negative
camber. Even with granny driving, there will be that emergency, kid
chasing a ball, etc., requiring an evasive maneuver. Having more
cornering G force at your disposal€”via the more complete
tread/pavement contact afforded by the €œpreload€� that negative camber
generates€” is always a good thing.

What they don't say is that negative camber will decrease the slip angle
at the front wheels whilst leaving the rear as standard. That will lead
to a snap oversteering car and *granny* may find that more than a little
disconcerting.


You are worried about "snap oversteer" at under 30 MPH - - - -

No but the car you correct for 30 MPH behaviour can easily become a pig
at 60 or 70 MPH. That's when the snap oversteer becomes a concern.

This camber scrub issue comes about because people want steering
stability at speed. Can't blame them for that and can't blame the
manufacturers for biasing their designs that way, especially when only a
very small percentage of drivers are going to see the extreme effects
that Arlen is seeing. My Toyota has it but not to any extent that I'm
going to swap tyres around on rims or anything like that. I'll just
replace the tyres a tad earlier than I usually do. I managed to get only
60,000 kilometres out of the first set where I would have expected my
more usual 80,000 kilometres that I was getting from previous Toyotas.
It's no big deal. What I did do is change my route slightly so I travel
a little further on my daily run but don't have to negotiate more than
one tight roundabout and rather more gentle bends. That little bit of
extra distance sure aggravates my wife though! ;-)

The settings recommended and designed in to the vehicle are a
compromize - designed for acceptable handling and tire wear under
"normal" conditions. Same with tire pressures.

Always. You can change the understeer/oversteer balance with tyre
pressures alone.

Which is why I recommended tire pressure check FIRST.

Under "abnormal" conditions - nose down, tight corners : you get both
squat and roll causing the camber to go positive - and you get weight
shift to the outside front corner, loading the outside front tire
significantly more than leveland straight driving - REQUIRING ahigher
tire pressure to "support" the load. It's the same as throwing 600
pounds into the trunk - only in reverse.


Regardless of the terminol;ogy (and I WAS wrong - and I admit it) the
SIMPLEST and MOST EFFECTIVE steps to reduce the tire wear a

#1 -check tire inflation and increase the front tire pressures -
basically to the spec for the rear tires fully loaded. - generally
about 5 to 10 PSI over the normal recommended tire pressure.
#2 - adjust the camber to 1 to 1.5 degrees more negative than spec if
possible.

This text is in full agreement with my diagnosis of Arlen's issue. His
issue is *camber Scrub* causes by *Camber Roll* during *tight turns* as
evidenced by the specific type of longitudinal feathering he is
experiencing on the outer shoulder of his tyres. It also supports the
partial solution that I offered, that he reduce his caster to the
minimum allowable specification. I have *known* of this issue for
*decades* but my current Toyota has given me my first personal
experience with it.

Not dissagreeing with your diagnosis

Thanks for that.

And I've dealt with it for years.About 90% of cars on the road are
running underinflated tires. PERHAPS just running the recommended
pressure may reduce the problem - IF the owner is allowing the
pressures to run too low - but a few extra PSI will NOT hurt - and
WILL help. I tend to drive a bit agressively - not as much as when
Iwas 50 years younger - and I ALWAYS run my front tires about 5 PSI
over spec - to prevent wearing the outer shoulders off my tires.

For a person who is an engineer, this book is a better start point.
https://www.springer.com/gp/book/9783319054483

As a followup, this one;
https://www.springer.com/gp/book/9783834809940

I have both the above and they make for very interesting reading.

For several years my road-going car was a 1972 Vauxhall Firenza. It
had several degrees of negative caster on an unequal length control

Sorry - I meant negative CAMBER

Ah, that explains it then.

Negative caster is unusual on a RWD car since it has the nasty effect of
increasing body roll, highly undesirable. Negative caster is more usual
on a FWD because of drive torque as opposed to rolling resistance but it
is kept to a bare minimum. It would be interesting to see all the
steering geometry specifications for that vehicle.

arm suspension, and it handled like it was on rails . With the wide

I presume you mean SLA front suspension.
Yes - short and long arm

Radial TA tires I had on it there was virtually NO tire wear over
almost 50,000 miles (between my driving and the friend I sold it to)

That will depend entirely on the type of driving you do. If it's a lot
of highway driving, no problem. Light urban driving, again no problem.

Pretty agressive driving - - It had a 2300cc OHC engine with twin
CD175 Strombergs. I rallied it a couple times when the Renault wasn't
ready to go. I also chased it up and down Mount Washington and around
the Cabot Trail. I lent tit to my best man when his Lotus Cortina was
out of commission. Guys with Lotus Cortinas didn't generally baby
them.

The Vauxhall Firenza never made it to these shores. I see it had a very
brief life - 3 years.

The USA got the Opel - we got the Vauxhall. Whether sold as a Viva HC
or a Firenza it was the same car. Also sold as the Magnum in the UK

Yep, badgework engineering. In that era we had Isuzus dressed up as our
local GM products.

The negative scrub radius helped tire wear and handling too, I
suspect. - - -

Definitely a safer way to go!

Our previous Toyota didn't show an issue but it was in an urban
environment most of its life. If you have lots of tight turns, as I have
experienced here and Arlen has experienced, you get camber scrub. It is
the compromise the manufacturers had to make given typical vehicle usage
patterns. Arlen's usage is not typical since he is doing lots of full
lock turns, grade notwithstanding. It is the full lock turns, with
attendant high positive camber gain on the inner wheel, that do the damage.

Along with the forward weight transfer and the centrifugal force
loading the outer tire. - and I agree - high positive camber gain -
not only from the tight lock, but also the squat and roll.

Most suspensions systems have a fair degree of anti-dive geometry built
into them these days so it's not the problem it was. Positive caster
jacks up the outer wheel so that should counter it as well.

Suspension systems, the SLA in particular, allow (cause) the front
camber to change under deflection. With an SLA front suspension at
normal ride height, the camber is at its static setting. Assume its
static setting is 0, neither negative or positive. As the wheel is
deflected up over a bump, the short arm will track a smaller radius than
the longer lower arm. This means the upper ball joint will be pulled
inwards at a greater rate than the lower ball joint. Because of this,
the camber actually goes more negative as the suspension is deflected
upwards. The benefit of this is that track width doesn't change under
single or two wheel deflection since the tyre at the contact patch
maintains its fore and aft alignment. Under body roll in a turn, the
inner mount of the upper arm may track outwards. This would normally
cause a camber change to the positive but, because of the short arm's
negative effect on camber change, the effect of each cancels the other
out and camber remains at or close to the static setting. IOW, the wheel
remains close to vertical and the contact patch and slip angles are
minimally affected. This is one of the reasons the racing fraternity
prefer SLA suspensions in either 4 link or 5 link varieties.

And the sla suspension is designed to do what I am recommending to do
- but just not enough for THIS situation. By starting with a static
negative you are just helping the factory design do a better job.

https://www.imperial.ac.uk/news/imag...2012/21320.jpg

Note too that the action depicted above by the SLA suspension is in
straight ahead situations. It does not take into account any camber roll
that occurs when the wheel is in a tight turn which, if the outside
wheel is already at a neutral camber, will cause it to become decidedly
negative.


Which is what you want - and adding an extra 1.5 degrees or so can
only help
One thing I have learnt about steering and suspensions over the years,
the more you learn, the more you realise you don't know.


"If I knew then what I know now I wouldn't know what I know now"



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On Fri, 21 Jun 2019 01:11:25 +1000, Xeno wrote:

No but, as stated, that particular feathered tread effect was pretty
unequivocal as to its cause.

I thank you, Xeno (and Clare) for UNDERSTANDING my particular issue.

I'm not actively participating simply because I'm embarrassed that I can't
add any additional value, in that I can _read_ what Xeno (and Clare) say,
and I can understand what they say, but when I've been driving the road
daily (multiple times), I keep trying to _imagine_ what is happening, while
I'm taking those turns with steering wheel inputs of
o Mostly 90 degrees each way (some less, some more)
o Some almost 360 steering wheel inputs
o Some even 90 degrees more than 360 degree steering inputs
All at around 20, to 30, to 40 (but no higher) speeds.

I did air up the tires, in an attempt to keep the tread more "firm", where
I will check front camber & caster separately (I need the tools first).

I picked up what seems to be a great free accelerometer graphical tool
o Sensors Multitool, version 1.3.2, by Wered Software
https://play.google.com/store/apps/details?id=com.wered.sensorsmultitool

Here's a screenshot of the output on my Android device but I need to test
it further before making any "lateral acceleration" claims ... where I'm
not sure exactly yet how to test other than to put the phone on the seat as
I drive downhill (uphill seems to have lesser forces for some reason).
https://i.postimg.cc/7hPhBY5b/accelerate01.jpg

I'm not sure yet how to interpret the difference between
o acceleration
o linear acceleration
Given what I want is
o lateral acceleration
https://i.postimg.cc/qqZJjcfZ/accelerate02.jpg

On 22/6/19 4:56 am, Arlen G. Holder wrote:
On Fri, 21 Jun 2019 01:11:25 +1000, Xeno wrote:

No but, as stated, that particular feathered tread effect was pretty
unequivocal as to its cause.

I thank you, Xeno (and Clare) for UNDERSTANDING my particular issue.

I'm not actively participating simply because I'm embarrassed that I can't
add any additional value, in that I can _read_ what Xeno (and Clare) say,
and I can understand what they say, but when I've been driving the road
daily (multiple times), I keep trying to _imagine_ what is happening, while
I'm taking those turns with steering wheel inputs of
o Mostly 90 degrees each way (some less, some more)
o Some almost 360 steering wheel inputs
o Some even 90 degrees more than 360 degree steering inputs
All at around 20, to 30, to 40 (but no higher) speeds.

Just turn your wheels to the full lock whilst parked on a flat surface.
Then get out and look at the steering angles, in particular the camber
on the front inside wheel. Then imagine what is happening at the tread
blocks at that inside wheel noting that they do not follow a straight
path when driving with the wheel at that steer angle, camber and lateral
acceleration.
BTW, page 348 of the above linked book depicts the type of tyre
deformation I am on about. It applies to zero camber events however. Try
to imagine what it will look like if the tyre is up on one (outer) edge
and pressing hard on the tread shoulder.

I did air up the tires, in an attempt to keep the tread more "firm", where
I will check front camber & caster separately (I need the tools first).

I picked up what seems to be a great free accelerometer graphical tool
o Sensors Multitool, version 1.3.2, by Wered Software
https://play.google.com/store/apps/details?id=com.wered.sensorsmultitool

Here's a screenshot of the output on my Android device but I need to test
it further before making any "lateral acceleration" claims ... where I'm
not sure exactly yet how to test other than to put the phone on the seat as
I drive downhill (uphill seems to have lesser forces for some reason).
https://i.postimg.cc/7hPhBY5b/accelerate01.jpg

I'm not sure yet how to interpret the difference between
o acceleration
o linear acceleration
Given what I want is
o lateral acceleration
https://i.postimg.cc/qqZJjcfZ/accelerate02.jpg



--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On 22/6/19 8:57 am, Xeno wrote:
On 22/6/19 4:56 am, Arlen G. Holder wrote:
On Fri, 21 Jun 2019 01:11:25 +1000, Xeno wrote:

No but, as stated, that particular feathered tread effect was pretty
unequivocal as to its cause.

I thank you, Xeno (and Clare) for UNDERSTANDING my particular issue.

I'm not actively participating simply because I'm embarrassed that I
can't
add any additional value, in that I can _read_ what Xeno (and Clare) say,
and I can understand what they say, but when I've been driving the road
daily (multiple times), I keep trying to _imagine_ what is happening,
while
I'm taking those turns with steering wheel inputs of
o Mostly 90 degrees each way (some less, some more)
o Some almost 360 steering wheel inputs
o Some even 90 degrees more than 360 degree steering inputs
All at around 20, to 30, to 40 (but no higher) speeds.

This link, forgot to put it in.

https://www.academia.edu/people/sear...hicle+dynamics

Thomas D. Gillespie-Fundamentals of Vehicle Dynamics -Society of
Automotive Engineers Inc (1992)

Just turn your wheels to the full lock whilst parked on a flat surface.
Then get out and look at the steering angles, in particular the camber
on the front inside wheel. Then imagine what is happening at the tread
blocks at that inside wheel noting that they do not follow a straight
path when driving with the wheel at that steer angle, camber and lateral
acceleration.
BTW, page 348 of the above linked book depicts the type of tyre
deformation I am on about. It applies to zero camber events however. Try
to imagine what it will look like if the tyre is up on one (outer) edge
and pressing hard on the tread shoulder.

I did air up the tires, in an attempt to keep the tread more "firm",
where
I will check front camber & caster separately (I need the tools first).

I picked up what seems to be a great free accelerometer graphical tool
o Sensors Multitool, version 1.3.2, by Wered Software

https://play.google.com/store/apps/details?id=com.wered.sensorsmultitool


Here's a screenshot of the output on my Android device but I need to test
it further before making any "lateral acceleration" claims ... where I'm
not sure exactly yet how to test other than to put the phone on the
seat as
I drive downhill (uphill seems to have lesser forces for some reason).
https://i.postimg.cc/7hPhBY5b/accelerate01.jpg

I'm not sure yet how to interpret the difference between
o acceleration
o linear acceleration
Given what I want is
o lateral acceleration
https://i.postimg.cc/qqZJjcfZ/accelerate02.jpg





--

Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

On Sat, 22 Jun 2019 08:59:29 +1000, Xeno wrote:

This link, forgot to put it in.
https://www.academia.edu/people/sear...hicle+dynamics

Hi Xeno,
I much appreciate that you UNDERSTAND the complex geometric changes that
occur during camber scrub low-speed lock-to-lock conditions, where we both
agree the specific phenomenon I am troubleshooting is a specific very
mountainous situation which isn't covered well on the net, but which does
have pragmatic workarounds, as you & Clave have discussed.

Here's a shot from today with the vehicle parked at one of the curves.
o Passenger tire at (static) steering-wheel lock, heading uphill:
https://i.postimg.cc/T1HkcsX5/mount31.jpg
o Driver side tire at that same wheel lock situation:
https://i.postimg.cc/KYXHVC3n/mount32.jpg

It's not easy to tell, but that inner tire (which is the one wearing the
most in these slow speed lock-to-lock turns) should be taking on a more
positive camber, while the outer tire should be taking on a more negative
camber.

Even though the outside tire is taking on more of the force, the wear is
happening more so to the outside shoulder of the inside tire (the tire with
the more positive camber). https://i.postimg.cc/YqHVb5gY/mount33.jpg

As you've explained it prior, at _slow_ speeds (30 mph nominally), there
isn't as much weight transfer to the outside wheel, and yet the inside
wheel is at a tighter lock than the outside wheel due to Ackerman Angle
effects, where the more positive camber on that inside wheel causes the
outside tread area to longitudinally feather unidirectionally more so than
the outside wheel, which takes on a lesser more positive camber.

Since we're effectively riding on the outside tread blocks of the inside
tire, those outside blocks are forced to break traction and slide, which is
what's causing the longitudinal unidirectional feathering, particularly
when traveling downhill.

Note that the passenger tire of this rather heavy bimmer SUV is the
original tire of only about a year and a half old (about 15K miles or so),
where the outside edge counter rotational longitudinal feathering is almost
worn away, but the driver's side tire had to be replaced a few months ago,
where the counter rotational longitudinal feathering is easily felt on the
outside few inches of the tread.

Am I correct that these are the possible ameliorations, bearing in mind
that every change made has an effect somewhere else in alignment and that
each change has to be made in the standard caster/camber/toe order?
1. First, increase tire pressure (to decrease tread squirm)
2. Second, potentially decrease positive caster (to the low end of spec)
(where the goal is to change how SAI affects the camber angle under turns)
3. Third, possibly (increase?) static negative camber (within spec)
(although increasing negative static camber "may" also decrease the SAI)
4. Set toe to spec last.
[If I got anything wrong, please let me know as it's confusing!]

Obviously this is a compromise, as weight shift, self centering and
steering forces may correspondingly change at speed, as you're well aware
from this video clip you prior suggested
https://youtu.be/VbReLNi2JP4?t=831

On Sat, 22 Jun 2019 08:17:00 -0000 (UTC), Arlen G. Holder wrote:

As you know, the camber changes dramatically...
https://www.quora.com/When-turning-I-see-there-is-a-plus-camber-in-a-vehicle-Why

The one thing I can't wrap my head around is that they say the positive
camber on inside tires when cornering turns into a NEGATIVE camber if just
the force vectors are considered.
https://i.postimg.cc/YqHVb5gY/mount33.jpg

What the heck does that mean?
I don't get it...