1997 Pontiac Trans Sport Owner's Manual - Page 369

Mixing tires could cause to lose control while you 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. Using tires of different sizes may also cause damage to your vehicle. Be sure touse the same size and type tires all wheels. on It's all right to drive with your compact spare, though. It was developed for use on your vehicle. car tires. The Uniform Tire QualityGrading system does not applyto deep tread, winter-type snow tires, use space-saver or temporary spare tires, tires with nominal rim diameters of 10 to 12 in'ches (25 to 30 cm), or to some limited-production tires. While the tires available on General Motors passenger cars andlight trucks may vary withrespect to these grades, they mustalso conform to Federal safety requirements andadditional General Motors Tire Performance Criteria (WC) standards. Treadwear The treadwear gradeis a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified governmenttest course. For example, atire graded 150 would wear one and a half (1 1/2) times as well on the government course as a tire graded 100. The relative performance of tires depends upon the actual conditionsof their use, however, and may depart significantly from the norm due to variations in driving habits, service practices and differences in road characteristics and climate. Uniform Tire QualityGrading The followinginformation 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 in the United States.)The sold grades are molded on the sidewalls af most passenger 6-44