1997 Chevrolet Blazer Owner's Manual - Page 300

I A CAUTION: Mixing tires could cause you to lose control while driving. If you mix tires of different sizes or types (radial andbias-belted tires), thevehicle may not handle properly, andyou 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 on all wheels. It's all rightto drive with your compact spare (if you have one). It was developed for use on your vehicle. 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-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. Treadwear The treadwear gradeis 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 graded 100. The relative performance of tires depends upon the actual conditions of their use, however, and may depart significantlyfrom the norm due to variations in driving habits, service practices and differences in road characteristics and climate. Uniform Tire Quality Grading The following information relates to system the 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