The following information relates to the system developed by the United States National Highway Traffic Safety Administration (NHTSA), which grades tires by treadwear, traction, and temperature performance. This applies only to vehicles sold in the United States. The grades are molded on the sidewalls of most passenger car tires. The Uniform Tire Quality Grading (UTQG) system does not apply to deep tread, winter tires, compact spare tires, tires with nominal rim diameters of 10 to 12 inches (25 to 30 cm), or to some limited-production tires.
While the tires available on General Motors passenger cars and light trucks may vary with respect to these grades, they must also conform to federal safety requirements and additional General Motors Tire Performance Criteria (TPC) standards.
Quality grades can be found where applicable on the tire sidewall between tread shoulder and maximum section width. For example:
Treadwear 200 Traction AA Temperature A
All Passenger Car Tires Must Conform to Federal Safety Requirements In Addition To These Grades.
Treadwear
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 one-half (1½) 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.
Traction
The traction grades, from highest to lowest, are AA, A, B, and C. Those 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 this tire is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning, or peak traction characteristics.
Temperature
The temperature grades are A (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 degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure. The grade C corresponds to a level of performance which all passenger car tires must meet under the Federal Motor Safety Standard No. 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 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.
Tire Inspection
We recommend that the tires, including the spare tire, if the vehicle has one,
be inspected for signs of wear or damage at least once a month.
Replace the tire if:
The indicators at three or more places around the tire can be seen.
There is cord or fabric showing through the tire's rubb ...
Shifting out of Park
This vehicle is equipped with a shift lock control. The shift lock control is
designed to:
Prevent ignition key removal unless the shift lever is in P (Park) with
the shift lever button fully released.
Prevent movement of the shift lever out of P (Park) unless the ignition
is in ON/RUN ...
Tire Designations
Tire Size
The following is an example of a typical passenger vehicle tire size.
(1) Passenger (P-Metric) Tire: The United States version of a metric tire sizing
system. The letter P as the first character in the tire size means a passenger vehicle
tire engineered to standards set by the U. ...