2009 GMC Envoy Owner's Manual - Page 364

High-Speed Operation { 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 P255/50R20 104V size tires installed on the rear axle, they will require inflation pressure adjustment when driving your vehicle at speeds above 99 mph (160 km/h). Set the cold inflation pressure, for the rear tires only, to the maximum inflation pressure shown on the tire sidewall, or 38 psi (262 kPa), whichever is lower. See the example following. When you end this high-speed driving, return the tires to the cold tire inflation pressure shown on the Tire and Loading Information label. See Loading the Vehicle on page 4-31. Example: You will find the maximum load and inflation pressure molded on the tire's sidewall, in small letters, near the rim flange. It will read something like this: Maximum load 690 kg (1521 lbs) 300 kPa (44 psi) Max. Press. For this example, you would set the inflation pressure for high-speed driving at 38 psi (262 kPa). The inflation pressure for the front tires should be set to the cold tire inflation pressure shown on the Tire and Loading Information label. Racing or other competitive driving may affect the warranty coverage of your vehicle. See your warranty booklet for more information. 5-62