ASTM F421-15(2021)

Standard Test Method for Measuring Groove and Void Depth in Passenger Car Tires

SIGNIFICANCE AND USE
5.1 The groove (void) depth affects the tire’s ability to develop tractive forces in various operating environments. Groove (void) depth also defines the state of wear of a tire and is used in the determination of the rate of wear.
SCOPE
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 be used, but 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.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2021
• ICS: 83.160.10 - Road vehicle tyres
• Technical Committee: F09 - Tires
• Drafting Committee: F09.30 - Laboratory (Non-Vehicular) Testing

Relations

• Refers: ASTM F1426-20 - Standard Practice for Identifying Tire Tread Surface Irregular Wear Patterns Resulting from Tire Use
• Effective Date: 01-Jan-2020
• Refers: ASTM F1426-11 - Standard Practice for Identifying Tire Tread Surface Irregular Wear Patterns Resulting from Tire Use
• Effective Date: 01-Nov-2011
• Refers: ASTM F538-09 - Standard Terminology Relating to the Characteristics and Performance of Tires
• Effective Date: 15-Jun-2009
• Refers: ASTM F538-03 - Standard Terminology Relating to the Characteristics and Performance of Tires
• Effective Date: 01-Dec-2003
• Refers: ASTM F1426-94(1999) - Standard Practice for Identifying Tire Tread Surface Irregular Wear Patterns Resulting from Tire Use
• Effective Date: 10-Sep-1999
• Refers: ASTM F538-99 - Standard Terminology Relating to the Characteristics and Performance of Tires
• Effective Date: 10-Apr-1999
• Refers: ASTM F1426-94(2003) - Standard Practice for Identifying Tire Tread Surface Irregular Wear Patterns Resulting from Tire Use
• Effective Date: 15-Jul-1994

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F421 − 15 (Reapproved 2021)
Standard Test Method for
Measuring Groove and Void Depth in Passenger Car Tires
ThisstandardisissuedunderthefixeddesignationF421;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 circumferential line, n— on a tire, any real or imagi-
nary circle on the surface of a tire, lying in a plane that is
1.1 This test method describes standard procedures for
perpendicular to the spin axis. F538
measuring the groove and void depth in passenger car tires.
3.1.2 element, n—an isolated (totally bounded by void)
1.2 Any mechanical, optical, or electronic device capable of
projection. F538
measuring groove (void) depth can be used, but only the
3.1.3 groove, n—a void that is relatively narrow compared
contact methodology is described here. Noncontact methodol-
to its length. F538
ogy is beyond the scope of this test method.
3.1.4 groove average depth, [L], n—the average of all tire
1.3 The values stated in SI units are to be regarded as the
groove depth measurements in a single groove. F538
standard. The values given in parentheses are for information
3.1.5 groove (void) depth, [L], n—a measurement of the
only.
perpendiculardistancefromarealorcalculatedreferenceplane
1.4 This standard does not purport to address all of the
defined by edges of two adjacent ribs (lugs) to the lowest point
safety concerns, if any, associated with its use. It is the
of contact in the groove (void).
responsibility of the user of this standard to establish appro-
3.1.5.1 Discussion—The reader is cautioned that the probe
priate safety, health, and environmental practices and deter-
tip used for the depth measurement must have a sufficiently
mine the applicability of regulatory limitations prior to use.
small cross-section compared to the width of the void being
1.5 This international standard was developed in accor-
measured. The probe must be able to reach the bottom of the
dance with internationally recognized principles on standard-
void without contacting the tread elements that form the sides
ization established in the Decision on Principles for the
of the void.
Development of International Standards, Guides and Recom-
Special consideration should be given to measuring sipes.
mendations issued by the World Trade Organization Technical
(See definition in Terminology F538.) Since the sipe is
Barriers to Trade (TBT) Committee.
substantially narrower than a major groove, a very small
2. Referenced Documents diameter probe tip must be used to achieve an accurate
measurement of sipe depth. F538
2.1 ASTM Standards:
3.1.6 irregular wear, n—a type of treadwear characterized
D4483 Practice for Evaluating Precision for Test Method
by substantial variations of tread loss both from projection to
Standards in the Rubber and Carbon Black Manufacturing
projection and frequently from point to point on a given
Industries
projection. F538
F538 Terminology Relating to the Characteristics and Per-
formance of Tires
3.1.7 projection, n—a pavement contacting area of the tread
F1426 Practice for Identifying Tire Tread Surface Irregular
band, bounded by void. F538
Wear Patterns Resulting from Tire Use
3.1.8 rib, n—a continuous circumferential projection. F538
3. Terminology 3.1.9 treadwear indicator, n—a raised portion of a groove
bottom or void bottom that is molded in a tire at fairly regular
3.1 Definitions:
intervals around the circumference to provide a visual indica-
tion that most of a tread has been worn away. F538
This test method is under the jurisdiction of ASTM Committee F09 on Tires
and is the direct responsibility of Subcommittee F09.30 on Laboratory (Non-
3.1.10 uniform wear, n—a type of treadwear characterized
Vehicular) Testing.
by equal tread loss both from projection to projection and from
Current edition approved April 1, 2021. Published April 2021. Originally
point to point on a given projection, resulting in a smooth
approved in 1975. Last previous edition approved in 2015 as F421 – 15. DOI:
appearance of all parts of the tread pattern. F538
10.1520/F0421-15R21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.11 void, n—a volume (in the tread band) defined by the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
lack of rubber, the depth dimension of this volume may vary
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. from point to point in (on) the tread band. F538
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F421 − 15 (2021)
4. Summary of Test Method 6.1.6 The accuracy shall be to within 0.025 mm (0.001 in.)
for distances up to 12.7 mm (0.5 in.) and to within 0.125 mm
4.1 This test method gives the detailed procedures and the
(0.005 in.) for distances from 12.7 to 25 mm (0.5 to 1 in.).
needed precautions for the measurement of the groove or void
6.1.7 The overall variability for a series of repeated mea-
depth of the tread pattern in a tire. Calculations for various
surements on the flat surface shall be within 620 % of one
types of average groove or void depths are given in addition to
division.
the required nomenclature for effective communication of the
6.1.8 Calibration shall be made using gauge blocks with
groove or void measurement results.
dimensions traceable to the National Institute of Standards and
Technology primary standard.
5. Significance and Use
5.1 The groove (void) depth affects the tire’s ability to
7. Preparation
develop tractive forces in various operating environments.
7.1 Gauge Zero Adjustment—Place the foot of the gauge
Groove (void) depth also defines the state of wear of a tire and
against a non-deformable flat surface such as a glass plate and
is used in the determination of the rate of wear.
adjust dial to zero.
6. Apparatus
7.2 Preparation of Tire:
6.1 Gauge:
7.2.1 Mount the tire on an approved width rim and inflate to
6.1.1 The apparatus shall consist of a mechanical or electro-
the required pressure.
mechanical depth gauge fitted with a foot through which a
7.2.2 The tire shall be in temperature equilibrium with the
spindle passes. The foot may have any of a variety of shapes,
environment in which it is measured.
including but not limited to cylindrical, semi-cylindrical, and
NOTE 1—For purposes of this test method, temperature equilibrium
rectangular. The reference surface of the foot shall be made of
exists if the gauge pressure remains within 7 kPa (1 psi) of the required
a non-deformable material, ground planar and perpendicular to
inflation pressure during the complete measurement process.
the gauge spindle. Examples of mechanical gauges and typical
7.2.3 The tire must be dry and free of any foreign material
available gauge feet are illustrated in Figs. 1 and 2. A typical
that would interfere with accurate measurement.
electro-mechanical gauge system is illustrated in Fig. 3.
7.2.4 Avoid the rubber vents on the t
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