GM Service Manual Online
For 1990-2009 cars only

Caution: Driving at high speeds, 100 mph (160 km/h) or higher, puts an additional strain on tires. Sustained high-speed driving causes excessive heat build up and can cause sudden tire failure. You could have a crash and you or others could be killed. Some high-speed rated tires require inflation pressure adjustment for high speed operation. When speed limits and road conditions are such that a vehicle can be driven at high speeds, make sure the tires are rated for high speed operation, in excellent condition, and set to the correct cold tire inflation pressure for the vehicle load.

If your vehicle has P265/65R18 or P285/45R22 size tires and you will be driving at high speeds, speeds of 100 mph (160 km/h) or higher, set the cold inflation pressure to 3 psi (20 kPa) above the recommended tire pressure shown on the Tire and Loading Information Label. When you end this high-speed driving, return the tires to the cold inflation pressure shown on the Tire and Loading Information label. See Loading the Vehicle and Inflation - Tire Pressure.