Re: Tire pressure to help dial out understeer
 

Hello Elroy,
The gentlemen at PES told me to run my front tires a couple
of pounds higher than the rear. right now I'm running 40 lbs.
in front and 38 lbs. at the rear. It's working out fine so far.
Kevin
01.5 S4

elroy@seedy-impaler.com wrote:

> On 20 Jun 2003 10:47:30 -0700, warp2_shadow@yahoo.com (C.R. Krieger)
> wrote:
>
>
>>Peter Bell <peter@bellfamily.org.uk> wrote in message news:<773771054c.peter@iyonix.earley.fourcom.com>. ..
>>
>>>Indeed, that has been my experience on some cars I have owned.
>>>However, the effect on handling of altering tyre pressures is a fairly
>>>complex issue, and depends on the setup of the rest of the car.
>>
>>No, it really isn't. To reduce the designed-in inherent understeer in
>>virtually all cars, one increases the front tire pressures relative to
>>the rear pressures. IOW, you can either reduce the rear pressures or
>>increase the front pressures, or both. To determine the window of
>>pressures in which to work requires a bit of experience, some educated
>>guesswork, and maybe the standerd autocrosser's trick of a bit of
>>chalk or shoe polish on the shoulders & sidewalls. [This is only to
>>measure rollunder - *do not* run it to the wheel or you'll look like a
>>total idiot. *Drag racers* run the lines to the wheel in order to see
>>wheelspin, not to see how much of the shoulder is being used in turns,
>>as autocrossers do.]
>>
>>Further, this general rule applies to *all* front vs. rear suspension
>>settings (anti-roll bars, springs, shocks, etc.). To reduce
>>understeer, one *stiffens* or *tightens* the front while *loosening*
>>the rear. To increase understeer (reduce oversteer), one does the
>>opposite.
>>
>>
>>> It
>>>isn't just the physical grip which determines this - the tyre
>>>effectively forms part of the suspension setup, affecting effective
>>>roll centre height.
>>
>>I think you're trying to make this more complicated than it really is.
>>Under- and oversteer is only indirectly (if at all - I have my
>>doubts) influenced by roll center height and, at best, tire pressures
>>can only affect this on a virtually undetectable level. Tire
>>pressures *do*, however, have a direct, discernible and immediate
>>effect on over- and understeer.
>
>
> Gentlemen,
>
> Thanks for all of the lively interaction. I have been trying a 43/38
> split since Sunday. I'm onMichelin Pilot Sports, and that seems to be
> a pretty good setting so far. I'll let everyone know in a month or so
> after my next outing.
>
> Regards,
>
> Elroy