1997 Pontiac Firebird Owner's Manual - Page 299

Mixing tires could cause to lose control while you sizes driving. If you mix tires of dif€erent or types (radi,aland bias-belted tires), the vehicle may not handle properly, and could have a crash. you Using tires of different sizes may also cause damage toyour vehicle. Besure to use the same size and type tires on all wheels. It's all right to drive with your compact spare, though. It was developed for use your vehicle. 0n car tires. The Uniform Tire Quality Grading system does not apply to deep tread, winter-type snow tires, space-saver or temporary use spare tires, tires with nominal rim diameters of 10 to 12 inches (25 to 30 cm), or to some lirnited-pro'duction tires. While the tires available on General Motors passenger cars and light trucks may vary with respect to these grades, they must also conform to Federal safety requirements and additional General MotorsTire performance Criteria (TPC) standards. Uniform Tire Quality Grading The following information relates to the system developed by the United States National Highway Traffic Safety Administration, which grades tires by treadwear, traction and temperature performance, (This applies only to vehicles sold in the United States.) The grades are molded on the sidewalls of most passenger Treadwear The treadwear grade isa comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear one and a half (1 1/2) times as well on the gov'esnrnentcourse as a tire graded 100. The relative performance of tires depends upon the actual conditions of their use, however, and may depart significantly from the norm due to variations in driving habits, service practicesand differences in road characteristics and climate. 6-54