1997 GMC Jimmy Owner's Manual - Page 304

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 havea crash. Using tires of different sizes may also cause damage toyour vehicle. Be sure touse the same size and type tireson all wheels. It's all right to drive with your compact spare use (if you have one). It was developed for on your vehicle. not apply to deep tread, winter-type snow tires, space-saver or temporary use spare tires, tires with nominal r i m diameters of 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 c Urades, they rnust also conform toFederal safety requirements and additional General Motors Tire Performance Criteria (TPC) standards. Treadwear The treadwear grade is a 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 government course as a tire e oraded 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 practices and differences in road characteristics and clilnate. 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 car tires. The Uniform Tire Quality Grading system does 6-45