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)