On Michelin® tires, DOT Quality Grades stand for U.S. Department of Transportation Quality Grades, or the Uniform Tire Quality Grading (UTQG). This is a tire information system designed to help you make relative comparisons between a single manufacturer’s passenger car tires (e.g., comparing one Michelin tire with another Michelin tire), except for: deep-tread, winter-type snow tires; space-saver or temporary use spares; or tires with normal rim diameters of 12 inches or less.
Under UTQG, tires are graded by the manufacturer in three areas: treadwear, traction, and temperature resistance. (See below for explanations.) The UTQG is not a safety rating and not a guarantee that a tire will last for a prescribed number of miles or perform in a certain way. It simply gives you additional information to combine with other considerations, such as price, brand loyalty, and dealer recommendations.
The UTQG information can be found on two places on the tire: a label affixed to the tread, and molded into the sidewalls.
The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions. For example, a tire graded 150 would perform over one and a half (1.5) times as well 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. They represent the tire's ability to stop on wet pavement as measured under controlled conditions on test surfaces of asphalt and concrete. A tire marked C may have relatively poor traction performance. The traction grade assigned to this tire is based on braking (straight ahead) traction tests and does not include cornering (turning) traction.
The temperature grades from highest to lowest are A, B, and C. They represent 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 degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure. The grade C corresponds to a level of performance that all passenger car tires must meet under the Federal Motor Vehicle Safety Standard No.109. Grades A and B represent higher levels of performance on the laboratory test wheel than the minimum required by law. The temperature grade for this tire is established for a tire that is properly inflated and not overloaded. Excessive speed, underinflation, or excessive loading, either separately or in combination, can cause heat buildup and possible tire failure.