National Highway Traffic Safety Adminstration Tire Ratings
NHTSA rates more than 2,400 lines of tires to help the consumer select the right replacement or new tire. The rating system is know as the Uniform Tire Quality Grading System (UTQGS), which allows consumers to compare tire treadwear, traction performance, and temperature resistance. The federal government requires tire manufacturers to grade their tires in these three areas and place the information on the sidewall of the tire.
Treadware Ratings - Treadwear grades are an indication of a tire's relative wear rate. The higher the treadwear number is, the longer it should take for the tread to wear down. A control tire is assigned a grade of 100. Other tires are compared to the control tire. For example, a tire grade of 200 should wear twice as long as the control tire.
Traction Ratings - Traction grades are an indication of a tire's ability to stop on wet pavement. A higher graded tire should allow a car to stop on wet roads in a shorter distance than a tire with a lower grade. Traction is graded from highest to lowest as "AA", "A", "B", and "C".
Temperature Ratings - Temperature grades are an indication of a tire's resistance to heat. Sustained high temperature (for example, driving long distances in hot weather), can cause a tire to deteriorate, leading to blowouts and tread separation. From highest to lowest, a tire's resistance to heat is graded as "A", "B", or "C".