Treadwear, Traction and Temperature

The treadwear grade is a comparative rating

based on the wear of a tire when tested carefully under controlled conditions. For

example the useful tread on a tire graded 400 should last twice as long as a tire

graded 200. However, another tire manufacturer may grade a comparable design

300, so a grade of 150 would last just half as long under their grading scheme. The

lesson learned is to not use one manufacturer's grade versus the other, but instead

to compare tire grades within a given brand. Actual treadwear performance can vary

tremendously according to the tire's real-world use. Variations in driving habits,

service practices (most importantly air pressure maintenance), road conditions and

climate affect tire life.

Traction grades represent the tire's ability to stop on

wet pavement as measured under controlled conditions on asphalt and concrete test

surfaces. As of 1997, the traction grades from highest to lowest are "AA","A","B" and

"C". A tire graded "AA" may have relatively better traction performance than a tire

graded lower, based on straight-ahead braking tests. The grades do not take into

consideration the cornering or turning performance of a tire.

Temperature grades represent a tire's resistance to

heat and its ability to dissipate heat when tested under controlled laboratory test

conditions. The grades from highest to lowest are "A","B" and "C". The grade "C"

corresponds to the minimum performance required by federal safety standard.

Therefore, the "A" tire is the coolest running, and even though the "C" tire runs hotter

it does not mean it is unsafe. The temperature grade is established for a tire that is

properly inflated and not overloaded.

Source: http://www.discounttire.com/dtcs/infoTreadwear.do

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