1993 Pontiac Bonneville Owner's Manual - Page 254

I CAUTION rn Uniform Tire Quality A Mixing tires could causeyou to lose control while driving. If you mix tires of different sizes or types (radial and bias-belted tires), the vehicle may not handle properly, and you could have a crash. Be sure 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 limited use on your vehicle. Grading The following information relatesto the system developed by the United States National Highway Traffic Safety Administration whichgrades tires by treadwear, traction and temperature performance. (This applies only to vehicles sold in the United States.) Treadwear The treadwear grade is acomparative rating based on the wear rate the tire of when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear one and a half (1%) times as well on the government course as a tire graded 100. The relative performance of tires depends upon the actualconditions of their use, however, and may depart significantly from the normdue to variations in driving habits, service practices and differencesin road characteristics and climate. 253