1996 Pontiac Grand Am Owner's Manual - Page 263

Mixing tires could cause you to lose control while driving. I you mix tires of different sizes or types f (radial andbias-belted tires), the vehicle may not handle properly, and you could.have a crash. Using tires of different sizes mayalso cause damage to yourvehicle. Be sure to use the same size and type tires on all four wheels. It's all right to drive with your compact spare, though. It was developedfor use on your vehicle. car tires. The Uniform Tire Quality Grading system does not apply to deep tread, winter-type snow tires, space-saver ortemporqy use spare tires, tires with nominal rim diametersof 10 to 12 inches (25 to 30 cm), or to some limited-production 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 Motors Tire 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 onlyto'vehicles sold in the United States.) The grades are molded on the sidewalls most passenger of Treadwear The treadwear grade is a comparative rating based on of the wear rate the tire when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear and a half one (1 1/2) times as well on the government course as a tire graded 100. The relative performance of'tires depends upon the actual conditions their use, however, and of may depart significantlyfrom the normdue to variations in driving habits, service practices and differences in road characteristics and climate. "