2005 Pontiac GTO Owner's Manual - Page 247

Be sure to put the valve caps back on the valve stems. They help prevent leaks by keeping out dirt and moisture. High Speed Operation Vehicles equipped with 245/45ZR17 95W size tires, do not require additional air pressure for high-speed operation. If your vehicle has 235/40ZR18 91W size tires, use the following chart to determine the cold tire inflation pressure when operating your vehicle under high-speed conditions. Tire Size: 235/40ZR18 91W Recommended Cold Tire Inflation Pressure for High Speed Operation Occupant and Cargo Weight: Occupant and Up to 740 lbs (330 kg) Cargo Weight: (Vehicle Capacity 470 lbs (210 kg) or less Weight) Front Tires Rear Tires Front Tires Rear Tires 36 psi 39 psi 44 psi 36 psi (250 kPa) (250 kPa) (270 kPa) (300 kPa) When you end high-speed driving, return the tires to the cold inflation pressure shown on the tire and loading information label. {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. 5-61