Tuning with tire temperatures

[Bart Carter]

Tire temperatures indicate how your tires are stressed.  The harder a portion of your tire is
working, the hotter it gets.  Temperature ranges will vary due to track conditions and the
tires you are evaluating, but should not go much over 200 degrees F.  You can use tire
temperatures to evaluate alignment, tire pressures, front to rear balance, tire and wheel
selection and more.

You can find a tire pyrometer at various places, usually at places that sell racing equipment.
If you don't have a favorite place, I have found that Racers Wholesale  is a good
company to deal with.  I would get a pyrometer that has almost instantaneous readings.
You shouldn't have to spend more than $100.

In testing you want to measure the temperatures that are created during cornering.  A skid
pad is the best format.  If you take temps after an autocross or race, you are measuring a
combination of LH and RH corners and straights.  You need a large expanse of asphalt.
Some have used a large parking lot that is not used at certain times.  You may need to get
permission.  Also check local race tracks, airports, etc.  Check in your area for clubs that put
on autocrosses or such for recommendations.  Always test under conditions that won't result
in any danger if something unexpected happens.  Make sure the car you are testing can
provide enough oil pressure under continued lateral forces.

Record keeping is important.  Make a chart and keep track of the changes.  Before beginning,
take your tire pressures, measure your tread depth and take tire temperature readings.  Take
temperature measurements across the treads of your front and rear outside tires.  Measure on
solid rubber areas at the inside, center and outside of each tread.  Make any other appropriate
notes such as skid pad surface conditions.

Draw a large radius circle on the skid pad.  This helps in consistency for better readings.   Try
to keep your car centered on the drawn circle.  Gradually increase your speed until you are at
the limits of your tires.  Be as smooth as possible so your suspension will settle and you won't
introduce other factors in your testing.  Make at least 5 laps at speed.  Stop and quickly take
temperature measurements of your front and rear outside tires.  Then take your tire pressures.
Alternate directions and make sure your records reflect direction of testing.

Interpreting results--
For correct camber you want the two edges of the tread to have the same temperature.  For
correct tire pressure you want the center of the tread to equal the average of the two edges'
temperatures.  The car's handling is balanced if the front and rear tires on the same side have
similar temperatures.  For example--

Tire Temperatures             Condition
Inside   Center   Outside     Camber         Pressure
190      190      190         Correct        Correct
180      190      180         Correct        High
195      190      185         Too negative   Correct
165      195      185         Too positive   High
105      145      215         Too positive   Low

Make adjustments and run again.  (See "Handling Adjustments" thread.)  Make sure you
record all data and results.  You may not be able to make some adjustments.  Make those that
are available to you.  You may have to compromise unless you want to make a larger
commitment.  The worst that will happen is that you will know the tire temperatures that will
give you the best handling with your car.

If you later are running on a surface that has more or less traction than the test surface, you
will have to make adjustments for that surface.  If you have adjustable front and rear anti-roll
bars, this may be fairly simple.  You may have to adjust your tire pressures for the new
surface.  The more you test and record the results, the easier it will be to make corrections
for different conditions.

I recommend improving the end of the car with the least grip to approach the end with the
most grip.  Remember that many changes affect both ends of your car.  I personally like a
very slight understeer that will allow steering with the throttle and won't give me too much
trailing-throttle oversteer.

[Bart Carter]

There is a companion post called "Handling Adjustments."

This will help decide what to do with the temperature data.

[Bart Carter]

A better site for Racer Wholesale is Racer Parts Wholesale

[Bart Carter]

If you are choosing between a probe type of pyrometer and an infrared type, my first choice would be a probe. It gets under the surface for a sightly more accurate reading.