ASTM F870-23

Standard Practice for Tread Footprints of Passenger Car Tires Groove Area Fraction and Dimensional Measurements

SIGNIFICANCE AND USE
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.
SCOPE
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, 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: 30-Apr-2023
• ICS: 83.160.10 - Road vehicle tyres
• Technical Committee: F09 - Tires
• Drafting Committee: F09.30 - Laboratory (Non-Vehicular) Testing

Relations

• 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 F538-99 - Standard Terminology Relating to the Characteristics and Performance of Tires
• Effective Date: 10-Apr-1999

Overview

ASTM F870-23 is the standard practice established by ASTM International for measuring the tread footprint characteristics of passenger car tires, specifically focusing on the groove area fraction and dimensional measurements. This standard outlines a practical approach for determining the percentage of void or groove area within the tire footprint, which is directly tied to essential performance parameters, such as traction and wear behavior, especially under wet or snow-covered conditions.

By providing defined laboratory procedures and ensuring measurements under controlled conditions, ASTM F870-23 supports the tire industry and testing laboratories in delivering accurate, consistent, and reproducible data for tire evaluation.

Key Topics

• Tire Tread Footprint: The process centers on measuring the area where the tire physically contacts a flat surface under load, using an inked impression on heavyweight paper.
• Groove or Void Area Fraction: Calculation of the ratio between the void area (non-contact regions defined by grooves and notches) and the gross footprint area, typically evaluated in the central 60% of the impression to avoid subjective end definitions.
• Dimensional Measurements: Assessments of footprint width, length, and gross area to support further evaluation of tire performance attributes.
• Standard Practice Methodology: Emphasizes a cut-and-weigh technique, but acknowledges the use of more advanced image analysis technologies for those with access.
• Reproducibility and Consistency: Defines precision expectations for interlaboratory measurement comparison, supporting reliable quality control and R&D processes.
• Reporting and Documentation: Details the requirements for thorough data reporting, including all relevant test parameters, tire identification, and zone locations.

Applications

• Tire Design and Development: Automotive engineers and tire manufacturers utilize these measurements when designing tread patterns to ensure optimal traction and wear characteristics.
• Quality Control: Laboratories and manufacturers implement this standard to monitor production consistency and verify that tires meet industry and regulatory requirements.
• Performance Benchmarking: Comparative analyses of different tire models or brands leverage the groove area fraction as a key performance metric.
• Research and Testing: Academic and industrial research into tire performance, including traction in wet and snowy conditions, often references this standard to ensure reproducibility and comparability.
• Regulatory Compliance: Provides a recognized, international method for groove area and footprint assessment, supporting compliance with regional and global standards.

Related Standards

• ASTM F538: Terminology Relating to Characteristics and Performance of Tires - a foundational reference for technical terms.
• Tire and Rim Association standards (TRA), ETRTO, JATMA: Regional standards providing guidelines on rim mounting and inflation for accurate testing.
• ISO and Other ASTM Tire Standards: Supports harmonization and cross-compatibility with other measurement and testing methodologies.

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Keywords: ASTM F870-23, tire tread footprint, groove area fraction, passenger car tire testing, tire dimensional measurement, tire performance, laboratory tire testing, void area measurement, quality control, traction performance, standard practice for tires.

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: F870 − 23
Standard Practice for
Tread Footprints of Passenger Car Tires Groove Area
Fraction and Dimensional Measurements
This standard is issued under the fixed designation F870; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Terminology
3.1 Definitions:
1.1 This practice covers a technique for measuring the
3.1.1 circumferential line, n—on a tire, any real or imagi-
groove or void area of a tire tread pattern. The void area is
nary circle on the surface of a tire, lying in a plane that is
measured on the inked impression of a tire tread statically
perpendicular to the spin axis. (F538)
loaded against heavyweight paper on a load platen.
3.1.2 developed footprint length, [L], n—the maximum
1.2 This procedure is intended to serve as a reference
footprint dimension in the circumferential direction of the tire,
practice for measuring groove or tread pattern void areas in a
under stated conditions of measurement.
tire-footprint impression. This technique is usable by any
3.1.3 developed footprint width, [L], n—the maximum lat-
laboratory without special equipment although more sophisti-
cated procedures are also commonly employed, such as optical eral dimension of a tire footprint under stated conditions of
measurement. (F538)
or video camera processes.
3.1.4 element, n—an isolated (totally bounded by void)
1.3 The values stated in SI units are to be regarded as the
projection. (F538)
standard. The values given in parentheses are for information
only. 3.1.5 footprint area, [L ], n—the gross contact area of a tire
that is loaded (under stated conditions) against a smooth flat
1.4 This standard does not purport to address all of the
surface. (F538)
safety concerns, if any, associated with its use. It is the
3.1.6 groove, n—a void that is relatively narrow compared
responsibility of the user of this standard to establish appro-
to its length. (F538)
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3.1.7 groove (void) area, [L ], n—that portion of tire foot-
1.5 This international standard was developed in accor- print area that is not contacted by ribs or elements.
dance with internationally recognized principles on standard-
3.1.8 groove (void) area fraction, [nd], n—the ratio of the
ization established in the Decision on Principles for the
groove (void) area to the footprint area of a tire. (F538)
Development of International Standards, Guides and Recom-
3.1.9 kerf, n—synonym for sipe. (F538)
mendations issued by the World Trade Organization Technical
3.1.10 lateral groove, n—a groove that has its long dimen-
Barriers to Trade (TBT) Committee.
sion oriented at direction non-parallel to the tire circumferen-
tial centerline; it most frequently opens into a void at both
2. Referenced Documents
ends. (F538)
2.1 ASTM Standards:
3.1.11 notch, n—a groove smaller in both width and length
F538 Terminology Relating to Characteristics and Perfor-
than a lateral groove, that contains one closed end. (F538)
mance of Tires
3.1.11.1 Discussion—For the purpose of this practice, it is
wider than 1 mm and more than 25 % as deep as a groove in
the same tire (see Fig. 1).
This practice is under the jurisdiction of ASTM Committee F09 on Tires and is
3.1.12 projection, n—a pavement contacting area of the
the direct responsibility of Subcommittee F09.30 on Laboratory (Non-Vehicular)
Testing. tread band, bounded by void. (F538)
Current edition approved May 1, 2023. Published June 2023. Originally
3.1.13 rib, n—a continuous circumferential projection.
approved in 1984. Last previous edition approved in 2016 as F870 – 94 (2016).
(F538)
DOI: 10.1520/F0870-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 2
3.1.14 rib or element area, [L ], n—that area within the
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
outer periphery of a tire footprint that is contacted by ribs or
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. elements.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F870 − 23
FIG. 2 Footprint Zones A, B and C
FIG. 1 Schematic Diagrams Kerf (Sipe) and Notch
3.1.15 sipe, n—a molded or cut rectangular void that is
substantially narrower than the major grooves or voids. (F538)
3.1.16 total or gross-contact area, [L ], n—that area encom-
passed by the outer periphery of a tire footprint.
3.1.17 void, n—a volume (in the tread band) defined by the
lack of rubber; the depth dimension of this volume may vary
from point to point in (on) the tread band. (F538)
4. Summary of Practice
FIG. 3 Definition of Shoulder Edge in Patterns That Do Not Con-
4.1 This practice is divided into two parts. Paragraph 8.1
tain a Solid Shoulder
provides a procedure to obtain a tire footprint impression.
Paragraph 8.2 describes the necessary measurements made on
the footprint impression, or copies thereof, to permit a calcu-
decisions are believed to be relevant, it is necessary that
lation of the groove-area fraction. Supplementary footprint
sufficient explanation be made in the final report.
width and length measurements may also be made.
6.2 One typical difficulty is illustrated in Fig. 2 in defining
4.2 The groove-area fraction is calculated from measure-
the outside shoulder edge of the footprint in tires that do not
ments in the central 60 % region of the footprint. This central
have a continuous well-defined shoulder rib edge. The total
60 % region (calculated from footprint length dimensions) is
area should be obtained by defining the edge of the print as
used to avoid the ambiguities and subjective judgements in
shown in Fig. 3.
precisely defining the “ends” of a footprint. The groove area
fraction, φ , is the ratio of the groove-void footprint area to the
A
7. Apparatus
total or gross-footprint area in this region. The gross area can
7.1 Tire Loading Machine—A machine or fixture that is
be obtained by direct measurement of this rectangular area.
capable of holding a rim-mounted tire vertically at normal
inflation pressures and that is capable of applying a specified
5. Significance and Use
tire load (within 62 %). The machine shall have a smooth, flat,
5.1 The tread of a tire, the annular band that contacts the
hard base upon which the tire is loaded. The rate of loading
pavement, normally contains geometric tread pattern elements
shall be such that no tire bounce or oscillation occurs upon
that are defined by grooves or voids. These are employed to
cessation of loading. Rates of vertical travel of 2 mm/s (4.7
confer appropriate traction properties to the tire, mainly on wet
in./min) or less in the loading operation are satisfactory.
or snow-covered roads.
7.2 Ink Pad—A soft, inked pad of sufficient area to apply ink
5.2 One characteristic feature of tire tread patterns that is
to the surface of the tread. An office foam-rubber stamp pad
important for both traction and tire wear behavior is the percent
used with stamp-pad ink is recommended. The pad shall be
or “fractional” groove area. The groove-area fraction is calcu-
inked so that the foam-pad material is fully saturated.
lated with respect to the total or gross contact area.
However, avoid excess ink, which frequently causes edge
distortions of the footprint impression.
6. Interferences
7.3 Footprint-Impression Paper—Paper of a size sufficient
6.1 Certain difficulties may be encountered in making
to accommodate the inked footprint. The paper shall be smooth
groove-area fraction and footprint dimensional measurements.
and of sufficient weight (175 g per square meter or greater) to
These are principally concerned with decisions on what to
prevent surface buckling or crimping during the tire load
include as void area. Tires are designed with a multitude of
geometrical features that show up on the footprint as a void
area. Section 3 addresses these problems. Subjective judge-
A stamp pad 80 by 150 mm or larger, with black stamp pad ink, has been found
ments as to what to include cannot be avoided, and where such to be satisfactory.
F870 − 23
process. The ink should not smear or penetrate beyond the 8.1.7 Install the mounted tire and rim assembly in the
geometrically defined rib areas due to capillary or other similar loading machine or fixture. Locate the first footprint zone and
action. position in an upright orientation. Ink the tread region thor-
oughly with firm pressure pad application, over a circumfer-
NOTE 1—The use of pressure-sensitive paper is permissible if the user
ential arc of approximately 30 cm. Inspect the inked surface to
can demonstrate that the impression is clearly defined and equivalent to an
assure:
inked print.
8.1.7.1 That all rib projections are fully inked and wetted
8. Procedure
(Note 2).
8.1 Tire Footprint Impression:
8.1.7.2 That excess inking has not occurred as manifested
8.1.1 Mount the tire on an approved rim per the TRA Year
by a buildup of ink on the edges of the ribs.
Book or other regional tire and rim standards such as the
NOTE 2—To assure thorough wetting of the rubber with the ink, it may
European Tyre and Rim Technical Organization (ETRTO) or
be desirable to clean the tread surface with a hydrocarbon solvent (hexane,
the Japan Automotive Tyre Manufacturers’ Association
heptane) prior to inking. Allow the solvent to evaporate.
(JATMA) and inflate to the inflation pressure (see 8.1.2) for
8.1.8 Rotate the center of the inked zone to the midpoint of
the load selected. Inspect the tread surface for irregularities,
the footprint-loading position and, with the paper held in place
such as mold vent protrusions, and remove any found.
at its edges by tape, load the tire to the load corres
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F870 − 94 (Reapproved 2016) F870 − 23
Standard Practice for
Tread Footprints of Passenger Car Tires Groove Area
Fraction and Dimensional Measurements
This standard is issued under the fixed designation F870; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
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 healthsafety, 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.
2. Referenced Documents
2.1 ASTM Standards:
F538 Terminology Relating to Characteristics and Performance of Tires
3. Terminology
3.1 Definitions:
3.1.1 circumferential line, n—on a tire, any real or imaginary circle on the surface of a tire, lying in a plane that is perpendicular
to the spin axis. (F538)
3.1.2 developed footprint length, [L],n—the maximum footprint dimension in the circumferential direction of the tire, under stated
conditions of measurement.
This practice is under the jurisdiction of ASTM Committee F09 on Tires and is the direct responsibility of Subcommittee F09.30 on Laboratory (Non-Vehicular) Testing.
Current edition approved Jan. 1, 2016May 1, 2023. Published February 2016June 2023. Originally approved in 1984. Last previous edition approved in 20102016 as
F870 – 94 (2010).(2016). DOI: 10.1520/F0870-94R16.10.1520/F0870-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F870 − 23
3.1.3 developed footprint width, [L],n—the maximum lateral dimension of a tire footprint under stated conditions of measurement.
(F538)
3.1.4 element, n—an isolated (totally bounded by void) projection. (F538)
3.1.5 footprint area, [L ],n—the gross contact area of a tire that is loaded (under stated conditions) against a smooth flat surface.
(F538)
3.1.6 groove, n—a void that is relatively narrow compared to its length. (F538)
3.1.7 groove (void) area, [L ],n—that portion of tire footprint area that is not contacted by ribs or elements.
3.1.8 groove (void) area fraction, [nd],n—the ratio of the groove (void) area to the footprint area of a tire. (F538)
3.1.9 kerf, n—synonym for sipe. (F538)
3.1.10 lateral groove, n—a groove that has its long dimension oriented at direction non-parallel to the tire circumferential
centerline; it most frequently opens into a void at both ends. (F538)
3.1.11 notch, n—a groove smaller in both width and length than a lateral groove, that contains one closed end. (F538)
3.1.11.1 Discussion—
For the purpose of this practice, it is wider than 1 mm and more than 25 % as deep as a groove in the same tire (see Fig. 1).
3.1.12 projection, n—a pavement contacting area of the tread band, bounded by void. (F538)
3.1.13 rib, n—a continuous circumferential projection. (F538)
3.1.14 rib or element area, [L ],n—that area within the outer periphery of a tire footprint that is contacted by ribs or elements.
3.1.15 sipe, n—a molded or cut rectangular void that is substantially narrower than the major grooves or voids. (F538)
3.1.16 total or gross-contact area, [L ],n—that area encompassed by the outer periphery of a tire footprint.
3.1.17 void, n—a volume (in the tread band) defined by the lack of rubber; the depth dimension of this volume may vary from
point to point in (on) the tread band. (F538)
4. Summary of Practice
4.1 This practice is divided into two parts. Paragraph 8.1 provides a procedure to obtain a tire footprint impression. Paragraph 8.2
FIG. 1 Schematic Diagrams Kerf (Sipe) and Notch
F870 − 23
describes the necessary measurements made on the footprint impression, or copies thereof, to permit a calculation of the
groove-area fraction. Supplementary footprint width and length measurements may also be made.
4.2 The groove-area fraction is calculated from measurements in the central 60 % region of the footprint. This central 60 % region
(calculated from footprint length dimensions) is used to avoid the ambiguities and subjective judgements in precisely defining the
“ends” of a footprint. The groove area fraction, φ , is the ratio of the groove-void footprint area to the total or gross-footprint area
A
in this region. The gross area can be obtained by direct measurement of this rectangular area.
5. Significance and Use
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.
6. Interferences
6.1 Certain difficulties may be encountered in making groove-area fraction and footprint dimensional measurements. These are
principally concerned with decisions on what to include as void area. Tires are designed with a multitude of geometrical features
that show up on the footprint as a void area. Section 3 addresses these problems. Subjective judgements as to what to include
cannot be avoided, and where such decisions are believed to be relevant, it is necessary that sufficient explanation be made in the
final report.
6.2 One typical difficulty is illustrated in Fig. 2 in defining the outside shoulder edge of the footprint in tires that do not have a
continuous well-defined shoulder rib edge. The total area should be obtained by defining the edge of the print as shown in Fig.
3.
7. Apparatus
7.1 Tire Loading Machine—A machine or fixture that is capable of holding a rim-mounted tire vertically at normal inflation
pressures and that is capable of applying a specified tire load (within 62 %). The machine shall have a smooth, flat, hard base upon
which the tire is loaded. The rate of loading shall be such that no tire bounce or oscillation occurs upon cessation of loading. Rates
of vertical travel of 2 mm/s (4.7 in./min) or less in the loading operation are satisfactory.
7.2 Ink Pad—A soft, inked pad of sufficient area to apply ink to the surface of the tread. An office foam-rubber stamp pad used
with stamp-pad ink is recommended. The pad shall be inked so that the foam-pad material is fully saturated. However, avoid
excess ink, which frequently causes edge distortions of the footprint impression.
7.3 Footprint-Impression Paper—Paper of a size sufficient to accommodate the inked footprint. The paper shall be smooth and
FIG. 2 Footprint Zones A, B and C
A Carter foam-rubber stamp pad No. 2 (80 80 by 150 mm (3 by 6 in.)) and Carter stamp pad ink No. 414, manufactured by Dennison Carter Ink Company, 321 Fortune
Blvd., Milford, MA 01752, have or larger, with black stamp pad ink, has been found to be satisfactory.
Recording chart paper X-Y-1101-SPI, manufactured by Graphic Controls Corp., 189 Van Rensselaer St., Buffalo, NY 14201, has been found to be satisfactory.
F870 − 23
FIG. 3 Definition of Shoulder Edge in Patterns That Do Not Contain a Solid Shoulder
of sufficient thickness (or weight) weight (175 g per square meter or greater) to prevent surface buckling or crimping during the
tire load process. The ink should not smear or penetrate beyond the geometrically defined rib areas due to capillary or other similar
action.
NOTE 1—The use of pressure-sensitive paper is permissible if the user can demonstrate that the impression is clearly defined and equivalent to an inked
print.
8. Procedure
8.1 Tire Footprint Impression:
8.1.1 Mount the tire on the test rim specified by the Tire and Rim Association Yearbookan approved rim per the TRA Year Book
or other regional tire and rim standards such as the European Tyre and Rim Technical Organization (ETRTO) or the Japan
Automotive Tyre Manufacturers’ Association (JATMA) and inflate to the inflation pressure (see 8.1.2) for the load selected.
Inspect the tread surface for irregularities, such as mold vent protrusions, and remove any found.
8.1.2 In the absence of any specific recommendations for inflation pressure, inflate to the maximum inflation pressure which is
shown on the sidewall of the tire.
8.1.3 For tires with numerous mold-vent projections, buff the tread surface lightly with a power-belt sander using fine abrasive
paper. Do this with the inflated tire and rim assembly mounted on a power-driven spindle rotating at 10 to 15 r/min. Apply light
pressure when buffing, always moving the buffer laterally back and forth. A removal of 0.05 to 0.1 mm (0.002 to 0.004 in.) of tread
surface has been found to be satisfactory. There should be no change in tread contour d
...