ASTM F870-94(2016)

5.1 The tread of a tire, the annular band that contacts the pavement, normally contains geometric tread pattern elements that are defined by grooves or voids. These are employed to confer appropriate traction properties to the tire, mainly on wet or snow-covered roads.

5.2 One characteristic feature of tire tread patterns that is important for both traction and tire wear behavior is the percent or “fractional” groove area. The groove-area fraction is calculated with respect to the total or gross contact area.

1.1 This practice covers a technique for measuring the groove or void area of a tire tread pattern. The void area is measured on the inked impression of a tire tread statically loaded against heavyweight paper on a load platen.

1.2 This procedure is intended to serve as a reference practice for measuring groove or tread pattern void areas in a tire-footprint impression. This technique is usable by any laboratory without special equipment although more sophisticated procedures are also commonly employed, such as optical or video camera processes.

1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.