1995 GMC Sonoma Owner's Manual - Page 262

Uniform Tire Qua/ity 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.) Treadwear The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions ona specified government test course. For example, a tire graded 150 would wear one and a half (1 1/2) times as well onthe government course asa 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 and climate. Traciion - A, 4C The traction grades, from highestto lowest are:A, B, and C. They represent the tire's ability to stop onwet pavement as measured under controlled conditions onspecified government test surfacesof 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. Temperaiure -A, 9, C The temperature grades are (the highest), B, and C, representing the tire's A resistance to the generation of heat and its ability to dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperature can cause material of the tire to the degenerate and reduce tire life, excessive temperature can lead to and sudden tire failure. The grade corresponds to a level of performance C which all 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. 6-44