On 14/6/19 6:28 am, Arlen G. Holder wrote:
On Thu, 13 Jun 2019 17:11:14 +1000, Xeno wrote:

You can check the camber all you like but the answer is more likely in
the SAI angles and you will be able to do SFA about that.

Hi Xeno,

Thanks for your purposefully helpful advice on kingpin inclination angle
(aka steering axis inclination), and perhaps included angle, neither of
which have I delved into yet (as I'm starting with camber, which is the
basis for caster calculations, and where toe is relatively simple).
http://www.valleyofhastings.com/WheelAlignment2.pdf

Use the term Steering Axis Inclination (SAI) as your vehicle likely does
not have kingpins. They are only found on trucks these days. I am of the
old school so I still use KPI but I found, when teaching apprentices,
the term is meaningless to them because most have never seen kingpins
much less worked on a vehicle so equipped.

Other than Clare, you and maybe one or two other folks here are
knowledgeable in the important details of home alignment checks &
adjustments, where I don't usually disagree with anything you guys say, as
you know more than I do.

We have to remember a home DIY alignment check & adjust is sort of like
doing a DIY tuneup versus a complete engine overhaul
o A DIY caster/camber/toe check/adjust is to a professional alignment
o as a DIY tuneup is to a professional engine blueprinting overhaul

The fact is that the SIA is a "non adujstable" angle:
https://www.freeasestudyguides.com/included-angle.html

The fact it's not adjustable means it is in a different category than
o caster
o camber
o toe

SAI, to the serviceman, is a *diagnosis angle* in much the same way as
*toe out on turns* (TOOT) is a diagnosis angle. If your toe is correct
but TOOT is incorrect, you can be assured that you have something that
is *bent*, usually a steering arm. Note, you cannot *adjust* TOOT in
cars as it is *designed in* as part of the Ackermann Angle.

While SIA is not normally adjustable, looking this up anyway for more
insight, it seems SIA checks generally simply need yet _another_ magnetic
bubble gauge, much like the camber gauge apparently, but offset by 90
degrees, according to this cite:
o Checking the Steering Axis Inclination Angle
http://route66hotrodhigh.com/Inclination.html
Which says:
"To measure steering axis inclination, the method is identical to caster
measurement except that you use the steering axis inclination guage [sic]
which is at a 90 deg angle to the caster gauge. The wheel is turned 20 deg
inward. The steering axis inclination gauge is centered for 0 deg caster.
There is an adjustment screw on the back of the gauge that allows you to
set it for 0 deg. The wheel is then turned to 20 deg outward for a total
movement of 40 degrees. The steering axis inclination angle is read off the
gauge."

The key question is where to get that SIA gauge, which, apparently, can be
replaced with a normal magnetic caster gauge according to this patent:
o Device & method for measuring SAI on a steerable wheel (#4,546,548)
http://www.freepatentsonline.com/4546548.pdf

In short, if we're aligning a vehicle that we own and drive often, then we
don't have any reason to suspect SIA changes (which will only occur with
bent or worn parts), and hence, they aren't part of what typically changes
(which is caster, camber, and toe).
https://www.motor.com/magazinepdfs/062002_05.pdf

about type of use instead. If it is all city and suburban driving, tyre
wear on the outside of the tread can be considered 100% normal.

On this mountain, everyone wears tires sooner than people who drive in
flatland do, where there is just "something" horrific about five miles of
steep driving,

Steep driving, urban driving, same thing really. You are at a greater
lock more often, even at slow speed, than when you are out on the
highways and freeways.

Most seem to wear on the outside edge, which I still haven't figured out
exactly why.

The term is Camber Scrub, and it caused a particular type of feathered
wear (for and aft feather IIRC) on the outside of the tyre, but it isn't
caused by the *camber angle* per se. It is caused by what SAI does to
the camber angles in a turn. Here is a video clip describing *one* of
the reasons for SAI.

https://www.youtube.com/watch?v=IZLiP_37Oso

The narrator focuses on the need to reduce unwanted feedback through the
steering. No mention is made of the other major reasons for SAI and that
is steering self centering and torque steer reduction. There are a
number of factors involved in steering stability and self centering
including; SAI, Caster, Camber, mechanical trail and tyre trail.

In this video clip he mentions the self centering effect at the end. He
states that turning the steering forces the axle (and wheel) down and,
in effect, lifts the front of the car. That provides the self centering
effect as the weight of the car will tend to return the steering to its
central or straight ahead position. That downward force also creates a
change in the *camber angle*.

https://www.youtube.com/watch?v=IUcZ63unEyU

But it is the camber angle the wheel adopts when at the turn position,
caused by SAI, that causes *camber scrub*.

This clip https://www.youtube.com/watch?v=VbReLNi2JP4 provides a very
good description of the steering functions. Skip to 13:50 for a
graphical display of the camber angle change when turning.

The road is about 5 miles at about a 9 percent angle with very
many 180 degree and even 270 degree switchbacks, but the speeds are rather
slow, where the road is too narrow to even have panted centerlines and
where the nominal speed limit for such roads is 25mph.

Definitely camber scrub territory.

Given nobody drives 25 mph anywhere, we can figure it's something like 30
mph to 40 mph top speed but there's a lot of braking in between. Me? I just
put the tranny in neutral and roll down the entire five miles by giving up
potential energy, where I only brake when I must and I take the turns very
wide (as most people do) which helps maintain speed.

Somehow, _that_ process (which most people do, I think, but in gear most
likely), wears tires out like you can't believe, where tires get half the
stated mileage, as far as I can tell by aggregate conversations.

Do the same distance on straight roads and you will have fairly even
tyre wear.

Turn the wheels to a high level of lock and the obvious will confront
you. The type of feathering will tell you what the actual cause is.

I do admit that I can't 'read' a tire very well. I've tried, but rotations
screw up the readings, and certainly there can be multiple causes.

It takes practice and, since I haven't operated a wheel aligner for a
very long time, I am *out of practice* but I've had the priciples
hammered into me over the decades ably assisted by having taught the
principles for some 20 years.

The type of feathering I mostly see is the kind you can feel after only
about 1000 miles on the outside edge, for about 3 inches of tread, where
there is a sharp lip that is feathered into that outside tread that you can
only feel moving your hand clockwise over the front tire tread on the
outside 3 inches.

That sounds like camber scrub feathering - if I'm reading your
description correctly.

I need to learn more, but I think that's "normal" since it happens even
after I get a professional alignment. I'm due for one soon for a couple of

A *professional alignment* cannot fix a *symptom* that is considered
*normal* for the kind of driving you do. Any changes made to mitigate
camber scrub will cause a reduction in handling capability at speed.

cars, which is why, instead of paying the $150 per vehicle, which for the 3
cars I want to do first, will be almost five hundred bucks, I'd rather buy
the tools to do it myself for that same five hundred bucks.
o Caster gauge (to measure caster & calculate camber)
o Caster jig (to lock onto the wheel for the caster gauge to be accurate)
o Wheel plates (to move the wheels for adjustment under suspension loading)
o Toe plates (to enable single-person linear measurement to centerline)

After having discussed this with Clare in the past, I know we can redneck
some of that, but overall, those four items seem to be the key items needed
for a home DIY check/change of caster, camber, & toe, do you agree?

Yes, that is basically all the small service station had next door to
where I did my apprenticeship. You have missed the primary requisite
however - a guaranteed dead flat and level garage floor. Also a lock to
lock the steering wheel to the desired centre position;
https://i.ebayimg.com/images/g/sJIAA...58p/s-l225.jpg



--

Xeno


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