1995 GMC Yukon Owner's Manual - Page 341

A CAUTION: Mixing tires could cause you lose control while driving. you to If mix tiresof different sizes or types (radial and bias-belted tires), the vehicle may not handle properly, and you could havea crash. Be sure to use the same and type tires on all wheels. size four Uniform Tire QualityGrading 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 i n the United States.) 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 ( I 1 /2) times a s 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 i n road characteristics and climate. Traction - A, 8, C The traction grades, from highest to lowest are: A, 8, C. They represent and the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfims of asphalt and concrete. A tire marked C may have poor traction performance. Warning: The traction grade assigned to this tire is based on braking (straight-ahead) traction tests and does not include cornering (turning) traction. Temperature - A, B, C The temperature gradesare A (the highest). B. and C. representing the tire's resistance to the generation of heat and its ability t o dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperature can cause the lnaterial of the tire to degenerate and reduce tit-e life, and excessive temperature can lead to sudden tire failure. The grade C corresponds to a level of performance which a l l passenger car tires must meet under the Federal Motor Vehicle Safety Standard No. 109. Grades B and A represent higher levels of performance on the laboratory test wheel than the minimum required by law. 6-59