On 16/6/19 4:31 pm, Arlen G. Holder wrote:
On Sat, 15 Jun 2019 14:14:27 +1000, Xeno wrote:

You won't. Information on it is scarce since it is an undesired effect.
However, if you look at what the wheel is doing vis a vis camber during
high angle (note - not high speed) cornering, then you can visualise the
issue. Note too that tread blocks have a limited degree of flexibility
and, as such, are likely to exceed that during high angle cornering
resulting in tread scrubbing.

Hi Xeno,

While I don't race, our conditions are "extreme" enough, in that constant
incessant repeated nearly full back-to-back wheel locks are causing
"something" to scrape away rubber, so this "camber scrub" is intriguing.

That is also considered *extreme* even though you aren't doing it fast.

I snapped this photo of tires that I mounted about a month ago, which only
have about 1000 miles on them, where they clearly show this pattern which
"might" be what you've been referring to as "camber scrub".
https://i.postimg.cc/zvvyL2tq/mount24.jpg

Does _that_ feathering look like what you're referring to as "camber scrub"?

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. Now try to
imagine what those tread blocks are doing as they roll around in a tight
circle with heaps of camber gain. It's not pretty and, worse, there is
SFA you can do about it.

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

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.



--

Xeno


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