The purpose of this practice is to standardize the meaning and derivation of some terms and indexes that are commonly used to characterize treadwear.

5.1.1 There is no intent to recommend either of the two treadwear performance indexes: distance per unit loss of tread depth or loss of tread depth per distance unit.

1.1 This practice describes the elementary linear regression analysis of basic treadwear data as obtained according to Test Method F 421 and Test Method F 762.

1.2 The basic treadwear data are obtained as groove depth loss measurements by procedures described in Test Method F 421 after a series of test cycles (test distances under specified conditions) according to Test Method F 762.

1.3 A linear regression analysis is performed for the relationship between average tire tread depth and the test distance traveled by the test vehicle, on which the test tires are mounted. From this analysis a rate of wear is determined: groove depth loss per unit distance.

1.4 Linear treadwear is defined as an essentially constant rate of wear, after break-in, which results in a linear regression coefficient of determination, R², equal to or greater than 0.95 when obtained for a data set where the number of measurement intervals, n, is at least 3. Each measurement interval represents a specific test distance.

1.5 This practice is not applicable to the prediction of treadlife for tires that exhibit non-linear or irregular treadwear.

1.6 Evaluation parameters are given for both SI and inch-pound units; either may be used. The evaluation parameters as defined are ones typically used in the tire testing industry and no special claim is made for superiority of these parameters and terms over other terms and parameters that may be developed.