[Dominik]

racedeck,

I let the pressure drop by 6 psi to 31 psi before the start (for 17").
Once the tire is hot I leave it where it is.

But because it was very hot these days I should have reduced the pressure even more. Never tried. Now it's cold.

all,
obviously initial (cold) tire pressures vary from car to car, tire to tire and conditions. The tire engineers that are present on every bigger event are the ones to ask.
One of Carroll Smith's Books may help here as well. Try "Tune to Win". Someone borrowed them from me, so I do not know which one answers this question.

I could just mention how much I dropped pressure from the initial (cold) value that is listed in the owner's manual. That was about 6 psi with track temp of 107 F.

For my 15" on the Cobra I run 35 psi on the street.
Track: 25 psi rear, 30 psi front.

To cunfuse you even more:
my buddy's race car with 15" wheels runs with 14 to 16 psi (cold)with sliks.

So go out there, monitor all temperatures and pressures under the same conditions and how the car felt on the track.

Bring a temperature gun and time along!

Hope that helps,

Dominik