Proper pressure depends on many variables... (archive)

I run 35 psi with Michelin Pilot Sports.
Yout pressure requirements may vary.
The following is from the tire rack website.
The Chart didn't copy well, so go to the website If you need more info.

Air Pressure
Tires support the weight of your car, right ? Actually, they don't. The air pressure inside the tire is what supports the car. The tire is basically just a container to put the air in. The correct air pressure is required for good handling, traction and durability.

However, you can't just set it and forget it. In most parts of North America, fall and early winter months are the most critical times to check inflation pressures because the days are getting shorter and the temperatures are getting colder. And since air is a gas, it contracts when cooled.

For every 10 degrees fahrenheit change in ambient temperature, your tire's inflation pressure will change by about 1 psi. It will go down with lower temps, and up with higher temps. The typical difference between summer and winter temperatures, is about 50 degrees F. - which results in a loss of about 5 psi and will sacrifice handling, traction, durability, fun, and safety.

The tire pressure recommended in your vehicles owners manual or tire information sticker is a "cold" pressure, so it should be checked in the morning before you drive the car more than a few miles. And by the way, if you park in a heated or attached garage, you will "lose" pressure when you leave its warmth and venture out into the cold. You may want to add 1 psi for each 10 degree F. in difference to compensate.

Keep in mind that tires tend to lose about 1 psi per month, so check them often.

Tire Tech

Competition Tire Air Pressure
When racing on D.O.T. approved tires air pressure is a major consideration in tuning the handling of your car, especially in cases where suspension adjustments are limited. The chart below shows some of the changes you can make to change the balance of the car. Please note that the air pressure changes are different on the BFG Comp T/A R1 than most other tires due to the asymmetrical sidewall construction.

Guide To High Performance Handling
Adjustments Decrease Understeer Decrease Oversteer
Front Tire Pressure
All except BFG Comp T/A R1 Higher Lower
Rear Tire Pressure
All except BFG Comp T/A R1 Lower Higher
Adjustments Decrease Understeer Decrease Oversteer
Front Tire Pressure
BFG Comp T/A R1 Only Lower Higher
Rear Tire Pressure
BFG Comp T/A R1 Only Higher Lower
Adjustments Decrease Understeer Decrease Oversteer
Front Tire Section Larger Smaller
Rear Tire Section Smaller Larger
Front Wheel Camber More Negative More Positive
Rear Wheel Camber More Positive More Negative
Front Wheel Toe Toward Toe-Out Toward Toe-In
Rear Wheel Toe Toward Toe-In Toward Toe-Out
Front Wheel Caster More Positive More Negative
Front Springs Soften Stiffen
Rear Springs Stiffen Soften
Front Anti-sway Bar Soften (Thinner) Stiffen (Thicken)
Rear Anti-sway Bar Stiffen (Thicker) Soften (Thinner)
Weight Distribution More Rearward More Forward

To get even tire wear when using D.O.T. tires you must be very careful not to use too low of a tire pressure. Both the BFG Comp T/A R1 and the Hoosier Radials can wear unevenly if underflated. The start point for the R1 should be close to the factory recommended pressures for your car, typically in the high 20's to mid 30's in psi. The Hoosier Radials seem to work best at much high pressures, such as the mid 30's to as high as 50 psi. If underinflated the R1's tend to wear near the first groove in from the outer shoulder, which has been termed the "Evil Groove O' Doom". On the Hoosier's, underinflation will cause a thin ring of wear at the very edge of the tread. The best results on the Hoosiers seem to come when they are properly inflated, on fairly wide wheels, and with a good amount of negative camber. If properly inflated, these problems can be avoided. Probably the biggest adjustment you can make to improve tire wear is the driver. Avoided sliding the tires, locking up the wheels under braking and drive as smooth as possible.

For both autocross and road racing, increase tire pressures 6-10 psi from what you would normally run in dry conditions. Hydroplaning occurs when a wedge of water develops between the tire and road surface. This wedge can actually lift the tire off the road and eliminate traction. Increasing the pressure rounds the profile of the tire by decreasing the deflection of the tire. This results in a smaller contact patch - narrower and shorter. It also helps keep the grooves in the tread open so they can channel the water out from under the tire.

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