Re: Suspension question Oversteer/Understeer?

["Owen" <mr.peepers@home.com>]

I know more based on experience (just from playing with different pressures
at the track) than from the physics side of things.  Basically i think there
are two elements to it.
   1.  Side wall stiffness.  if you have not enough pressure in the tire, it
will allow the sidewalls to flex, and the tires to roll over on themselves,
and you loose grip.  with more pressure you'll get a stiffer sidewall and
less flex, keeping more of the contact patch on the ground

   2.  the contact patch itself is controlled by a combination of pressure
and suspension geometry.  What helps you set this up is a pyrometer (tire
temp gauge) and a pressure gauge.  after each run you take tire temps (asap,
so the tires have no little time to cool down).  You take and outer, middle
and inside reading as well as pressure.  here is an example of what you
might get

                        O        M         I

                       95       103     117           Ok, you could
interpret this as having too much negative camber,

                       95        105    94             this would be an
instance where you are going to lower pressure.

                       95         80     95               here you would
want to raise the pressure.

                       110        90    89              If you get something
like this, you'll want to dial in a little more negative camber.

I hope that kind of explains it.  Basically your tire temps give you an idea
of how your tires are contactin the ground, and i guess you could say the
the hotter the temp, the more that part of the tire is contacting the ground
that others.
    you ultimatly want to have even temps all accross the tire.  then you
are getting full contact out of the tire.  raising and lowering the pressure
generally controls the middle of the tire.  if you overinflate, the tire
kinda baloons, and the middle bulges out, if you underinflate, the middle
sags, and the outer areas of the tire will tend to contact more.

Hope that makes sense, and will score you some new cars in Grand turismo :)


Owen
87 Scirocco 16v #38 C-SS.
http://www.geocities.com/MotorCity/Garage/1571


>How does the tire pressure thing work? I haven't done any auto racing, but
>if you're experiencing oversteer, you want more traction on the rear to
>balance the front, right? Wouldn't /lowering/ the rear air pressure (or
>raising the front) make the tires more supple/flexible, thus giving more
>traction?
>
>I noticed that both Andre' and Owen speak of raising the rear pressure.
>Considering that, IIRC, both you guys have racing experience, I'd believe
>what you say before my above logic. Could you explain how this works?
>
>I think I'm gonna have to go play with this in Gran Turismo and see what
>happens... Gawd that game rocks!
>
>Neal (playing the ignorant fool...again...)



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