Tire Size Conversion Chart
5/31/10 1:08 PMTire Tech - Tire Size Conversion Chart
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The Department of Transportation requires each manufacturer to grade its tires under the Uniform Tire
Quality Grade (UTQG) labeling system and establish ratings for treadwear, traction, and temperature
resistance. These tests are conducted independently by each manufacturer following government guidelines
to assign values that represent a comparison between the tested tire and a control tire. While traction and
temperature resistance ratings are specific performance levels, the treadwear ratings are assigned by the
manufacturers following field testing and are most accurate when comparing tires of the same brand.
Treadwear receives a comparative rating based on wear rate of the the tire in field testing following a
government specified course. For example, a tire grade of 150 wears 1.5 times as long as a tire graded 100.
Actual performance of the tire can vary significantly depending on conditions, driving habits, care, road
characteristics, and climate.
Straight-a-head wet braking traction has been represented by a grade of A, B, or C with A being the
highest. In 1997 a new top rating of "AA" has been introduced to indicate even greater wet braking traction.
However, due to its newness, this grade will probably be applied initially to new tire lines as they are
introduced and later to existing lines which excel in wet braking, but had been limited to the previous top
grade of "A". Traction grades do not indicate wet cornering ability.
Temperature resistance is graded A, B or C. It represents the tire's resistance to the heat generated by
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