ASTM F421-15 (R2021) pdf free download.Standard Test Method for Measuring Groove and Void Depth in Passenger Car Tires.
1.1 This test method describes standard procedures for measuring the groove and void depth in passenger car tires.
1.2 Any mechanical. optical, or electronic device capable of measuring groove (void) depth can he used, hut only the contact methodology is described here. Noncontact methodology is beyond the scope of this test method.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
3. 1 .5 groove (void) depth, n—a measurement of the perpendicular distance from a real or calculated reference plane defined by edges of two adjacent ribs (Jugs) to the lowest point of contact in the groove (void).
3.1.5.1 Discussion—The reader is cautioned that the probe tip used for the depth measurement must have a sufliciently small cross-section compared to the width of the void being measured. The probe must be able to reach the bottom of the void without contacting the tread elements that form the sides of the void.
Special consideration should be given to measuring sipes. (See definition in Terminology F538.) Since the sipe is substantially narrower than a major groove, a very small diameter probe tip must be used to achieve an accurate
measurement of sipe depth. F538
3.1.6 irregular weai n—a type of treadwear characterized by substantial variations of tread loss both from projection to projection and frequently from point to point on a given projection. F538
3.1.7 projection, n—a pavement contacting area of the tread hand, bounded by void. F538
3. 1 .8 rib, n—a continuous circumferential projection. F538
3.1.9 treadwear indicato,; n—a raised portion of a groove bottom or void bottom that is molded in a tire at fairly regular intervals around the circumference to provide a visual indication that most of a tread has been worn away. F538
3.1.10 uniform wear, n—a type of tread wear characterized by equal tread loss both from projection to projection and from point to point on a given projection. resulting in a smooth appearance of all parts of the tread pattern. F538
3.1.11 void, n—a volume (in the tread hand) defined by the lack of rubber, the depth dimension of this volume may vary from point to point in (on) the tread band.ASTM F421 pdf download.