Tire Maintenance

Understanding the Uniform Tire Quality Grading System


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The Uniform Tire Quality Grading System was adopted by the United States Department of Transportation’s National Highway Safety Administration in order to provide a more reliable means of grading overall tire quality. However, there are two main flaws with this system as set forth. These are that the tire companies are responsible for performing their own testing, and their tires are compared against control tires of their choosing. Tires are graded in three areas:

  • Temperature
  • Treadwear
  • Traction

Temperature

The temperature grading portion of the Uniform Tire Quality Grading System measures how well the tire deals with heat; how well it dissipates heat generated by the braking system and rotational friction; and how well the tire stands up to the heat generated during extended usage. This test is performed by running a properly inflated tire, under load, against a spinning test wheel of large diameter in the laboratory. All tires sold in the US must be able to pass this test with at least a grade of “C”, which means they are capable of performing at a minimum speed of 85 miles per hour. Grades and corresponding temperatures are listed below:

  • A-Over 115 MPH
  • B-Between 100 and 115 MPH
  • C-Between 85 and 100MPH

Traction Ratings

Traction ratings as specified using this tire comparison method are based on the specific tire’s coefficient of friction as it is pulled across a wet surface. Tested surfaces are wet asphalt and wet cement. Tires are mounted on a test trailer and pulled at a speed of 40 MPH across the test surface, where the brakes are momentarily applied, locking the brakes. The amount of skid is measured by the test trailer and a grade assigned. The less distance that the wheel skids for, the higher the grade assigned. Grades range from a C up to AA for high performance street and racing tires.

Treadwear Ratings

This is the single area of measurement where the most controversy has been generated. As stated before, there is no industry standard tire for use in this tire comparison. Comparison, or control, tires are called Course Monitoring Tires for this test. The DOT specifies that tires being tested are run on a special track in West Texas that is a 400 mile loop. These tires are mounted on cars in a convoy and run for 7,200 miles and checked. Tires can have air pressures set and adjusted during the test, as well as alignments performed during the test. Tires will be rotated every 800 miles. At the end of the 7,200 miles, the tires under test are compared to the “control tire” and graded using a percentage system. Thus, if a tire is rated as a 500, that means it is expected to be able to last five times as long as the test tire.

The Uniform Tire Quality Grading System has been generating great controversy in the tire industry since its inception a number of years ago. However, as a general guide for the purpose of getting a general idea of how well a given tire will perform, it comes in very handy.

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