The Federal Government Uniform Tire Quality Grading Standards (49 CFR 575.104) apply to passenger car tires only (but excludes deep tread, winter-type snow tires, temporary use spare tires, and tires with nominal rim diameters of twelve inches or
less). Tires subject to the Standards are required to be graded on the performance factors of treadwear, traction and temperature. The grades are molded on the tire sidewall, and in addition for replacement tires, a label affixed to the tread lists
and explains these grades. Tire characteristics defined in the Standards are as follows:
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 (1 1/2) times as 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 in
road characteristics and climate.
The traction grades, from highest to lowest, are AA, A, B and C. These grades 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 each tire is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning or peak traction characteristics.
The temperature grades are A (highest), B and C, representing the tire’s resistance to the generation of heat and it’s 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 degenerate and reduce tire life, and excess temperature can lead to sudden tire failure. The grade C corrosponds to a level of performance which all passenger car tires must meet under the Federal
Motor Vehicle Safety Standard # 109. Grades B and A represent higher levels of performance on the laboratory test wheel than the minimum required by law. WARNING: The temperature grade for each tire is established for a tire that is properly inflated
and not overloaded. Excessive speed, under inflation or excessive loading, either separately or in combination, can cause heat buildup and possible tire failure.
All Passenger Car Tires Must Conform to Federal Safety Requirements in Addition to These Grades.
Other factors affecting relative tire performance from one vehicle to another are: horsepower, automatic vs. manual transmission, gear ratios, etc.