[Race] RE: Tire Temperature (Long)

["Theodore W. Matthias" <twm@xxxxxxx>]

I have used a simple pyrometer with needle probe for suspension
and tire pressure tuning as an aid to autocross and street setups.
The pyrometer cost between $75 and $80.

I'm not an expert, but I had great success (as measured by my 
G.Analyst) in adjusting camber, shock settings and tire pressure.
These tips should be applicable to any automobile though front
drive (and some rear drive!) cars don't have a way to adjust
camber without shimming or replacing parts.

The method I used is very simplistic but a wealth of knowledge
exists in books and on the internet to expand (correct!)what is
presented below:

GOAL: Maximize and equalize all tires' contact patches.

After and autocross run (or spirited [legal] street driving), take
a temperature reading at three different points across the tire's
tread: outer, middle and inner readings.  The desired pressure/
suspension setup will produce temperature readings that vary little
from outer to inner.  Adjust the tire pressure first, then camber,
then shock settings.

TIRE PRESSURE:

Tire pressure problems (under/over-inflation) are reflected by the
outer/inner temperatures being higher or lower that the middle
temperature.  Example (hypothetical temperatures):

                        Left Front
                   Outer  Middle   Inner
                   |_________|_________|

 overinflation:    97       122       94
underinflation:    119       98      117
       optimal:    107      105      104

Vary inflation until the temperatures across the tread are as
close to the same as possible.  You may be suprised at how much
difference this simple procedure can make.


CAMBER:

After the tire pressure has been optimized, the need to adjust 
camber may be noticed by either the inner and outer temperatures
being significantly different from each other.  Example:

                              Left Front
                         Outer  Middle   Inner
                         |_________|_________|

need negative camber:    122      100       94
need positive camber:    97       102      119
             optimal:    107      105      104


SHOCK SETTINGS:

After tire pressure and camber have been optimized, the resulting
temperature profiles can be compared between tires.  Stiffening
the shock setting at a corner will tend to lower the tire 
temperatures at that corner.  Example:

                           Left Front              Left Rear
                      Outer  Middle   Inner   Outer  Middle   Inner
                      |_________|_________|   |_________|_________|

 before adjustment:   107      105      104   92       95        94
stiffen front left:   100       98       99   98       97        99


NOTE:

There are many other factors that enter in here.  What I have
illustrated is a "poor man's" approach to a very complicated subject.
But for less than $100, a pyrometer can yield very noticeable results
as well a maximizing investments made in aftermarket tires, wheels,
springs, shocks and other suspension related goodies.

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