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.