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I don't know if this applies for the track, but for autocross a good rule of thumb is to add 10 PSI to your street pressures (measured cold) as a starting point. Then you can chalk or shoe polish 3 or 4 points where the sidewall meets the tread and adjust pressures based on how much rollover you are getting on the sidewall.

Remember that up to a point adding pressure to a tire increases traction. If you are pushing, add pressure to the fronts (or decrease the rears). If you're loose, add pressure to the rears (or decrease the fronts).

Of course all bets are off if you're using R compound tires since the sidewalls are too firm to rollover and different pressure rules can apply. Then you need a pyrometer to measure the temp of the tires and adjust based on that.
 
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