1998 Chevrolet Express Van Owner's Manual - Page 286

TIION: If you usebias-ply tireson your vehicle, the wheel rim flanges could develop cracks after A many miles of driving. tire and/orwheel could fail suddenly, causing crash. Use only a radial-ply tires with the wheels on your vehicle. 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 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 graded 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 andclimate. 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 andtemperature performance. (This applies only to vehicles sold in the United States.) The grades are molded on thesidewalls of most passenger car tires. The Uniform Tire Quality Grading system does not apply to deep tread, winter-type snow tires, space-saver or temporary use spare tires, tires with nominal rimdiameters of 10 to 12 inches (25 to 30 cm), or to some limited-production tires.