Wheels and Tires Uniform Tire Quality Grading acceleration, cornering, hydroplaning or peak traction characteristics. The following information relates to the tire grading system developed by the National Temperature Highway Traffic Safety Administration (NHTSA), which grades tires by tread wear, The temperature grades are A (the highest), B, traction and temperature performance. Tires and C, representing the tire†s resistance to the that have deep tread, and winter tires, are generation of heat and its ability to dissipate exempt from these marking requirements. heat when tested under controlled conditions Where applicable, quality grades are found on on a specified indoor laboratory test wheel. the tire†s sidewall between the tread shoulder Sustained high temperature can cause the tire and maximum section width. For example: to degenerate and reduce tire life, and excessive temperature can lead to sudden tire • TREADWEAR 180 failure. • TRACTION AA The grade C corresponds to the minimum • TEMPERATURE A level of performance that all passenger car The quality grades are described next. tires must meet under the Federal Motor Safety Standard No. 109. Grades B and A Note: In addition to the marking requirements, represent levels of performance on the passenger car tires must conform to Federal laboratory test wheel that exceed the Safety Requirements. minimum requirements. Treadwear Warning: A tire†s temperature grade is established for a tire that is properly The treadwear grade is a comparative rating inflated and not overloaded. Excessive based on the wear rate of the tire when tested speed, under-inflation, or excessive under controlled conditions on a specified loading, either separately or in government test course. combination, can cause heat buildup and For example, a tire graded 150 wears one and possible tire failure. a half times better on a government test course than a tire graded 100. The relative performance of tires depends on the actual conditions of their use, however, and can depart significantly from the norm due to variations in driving habits, service practices, road characteristics, and climate. Traction The traction grades, from highest to lowest, are: AA, A, B, and C. These grades represent a tire†s ability to stop on wet pavement as measured under controlled conditions on test surfaces of asphalt and concrete. A tire marked C might have poor traction performance. Warning: Defective tires are dangerous. Do not drive if a tire is damaged, excessively worn, or is inflated to an incorrect pressure. The safety of the vehicle and occupants can be adversely affected. Check tires regularly for wear and to ensure there are no cuts, bulges or exposure of the ply/cord structure. Warning: The traction grade assigned to the tire is based on straight-ahead braking tests, and does not include: Specifications 141