1997 Buick Skylark Owner's Manual - Page 278

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 soldin the United States.)The grades are molded on the sidewallsmost passenger of 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 rm diameters of 10 to 12 inches (25 to 30 cm), i or to some limited-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 Federal safety to requirements and additional General Motors Tire Performance Criteria(PC) standards. Treadwear The treadwear grade is a comparative rating based on the wearrate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded would wear one and a half 150 (1 1/2) times as wellon the government course as a tire graded 100. The relative performanceof tires depends upon the actual conditions their use, however, and of may depart significantly from the normdue to variations in driving habits, service practices and differences in road characteristics and climate. Traction A, B, C The traction grades,from highest to lowest, are A, and B, C, and they represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. A tire marked C may have poor traction performance. Warning: The traction grade assigned to this tirebased is on braking (straightahead) traction tests and does not include cornering (turning) traction. -- 6-43