1998 Pontiac Grand Am Owner's Manual - Page 280

Treadwear The treadwear grade a comparative rating based is on the wear rate the tire when tested under controlled of conditions on a specified government test course. For example, a tire graded would wearone and a half 150 (1 1 2 times as well on the government course as tire 1) a graded 100. The relative performance tires depends of of upon the actual conditions their use, however, and may depart significantly from the norm to variations due in driving habits, service practices and differences in road characteristics and climate. Temperature -- A, B, C Traction -- A, B, C A The temperature grades are (the highest),B, and C, representing the tire's 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 the material of the tire to degenerateand reduce tire life, and excessive temperature can lead to sudden tire faiIure. of The gradeC corresponds to a level performance which all passenger car tires must meet under the No. Federal Motor Vehicle Safety Standard 109. Grades B and A represent higher levels performance onthe of laboratory test wheel than minimum required by law. the The traction grades, from highest to lowest, A, B, are Warning: The temperature grade for tire is this and C, and they represent the tire's ability to stop on wet established for a tire that is properly inflated and not pavement as measured under controlled conditions on overloaded. Excessive speed, underinflation, or of specified government test surfaces asphalt and excessive loading, either separately in combination, or concrete. A tire markedC may have poor traction can cause heat buildup and possible tire failure. performance. Warning: The traction grade assigned to this tire is based tests on braking (straight ahead) traction and does not include cornering (turning) traction. 6-47