Re: Tire wear, all-seasons, and stuff

[Todd Phenneger <phen9461@uidaho.edu>]

On Fri, 19 Feb 1999, Michael Williams wrote:

> > For the track I would up this to about 45 in back to induce more
> >Oversteer. 
> thats interesting, technically, this would increase understeer, not 
> oversteer...

	THats what I thought.  ANd you are partially right.  Increasing
tire press in rear does two things.  Changes contact patch and increases
wheel rate.  The increase in wheel rate alone would induce less understeet
but since the contact patch changes they have to work together.  I have
found that in MY car at ITS weight 42-44 lbs is about the optimum press
for grip.  I am thus assuming this is because at this level it has a good
contact patch, even weight dist through that contact patch, and enough
pressure to keep the tire from colapsing under force from the side loads.
If I inflate the rears above this then the tire has less contact patch or
at least is bulging a bit at the center and loses a "little" grip.  At the
same time coupled with the higher spring rate it tends to oversteer more
when I lift the throttle mid corner and is easier for me to rotate on the
track.
	I get a similar effect if I run a much lower pressure in the rear
but it isn't as controllable as it is just breaking loose from the
sidewalls rolling over to much and the tire deforming.  
	I have found the AWD car (at least mine) to be much harder to tune
with tire pressure than other cars such as Fwd/RWD as with those cars it
is more straight forward what to do.  
	Now, with different tires this may change but I "think" this is so
far the best set up I have found for my car.
	Anyone else BTDT with 4kq for Auto Cross or track use that has
experimented enoght with it with suspension settings the same to get an
accurate idea of what does what????
	Thanks
	
	Todd