ASTM F870-94(2016)
(Practice)Standard Practice for Tread Footprints of Passenger Car Tires Groove Area Fraction and Dimensional Measurements
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F870 − 94 (Reapproved 2016)
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 3.1.2 developed footprint length, [L], n—the maximum
footprint dimension in the circumferential direction of the tire,
1.1 This practice covers a technique for measuring the
under stated conditions of measurement.
groove or void area of a tire tread pattern. The void area is
3.1.3 developed footprint width, [L], n—the maximum lat-
measured on the inked impression of a tire tread statically
eral dimension of a tire footprint under stated conditions of
loaded against heavyweight paper on a load platen.
measurement. (F538)
1.2 This procedure is intended to serve as a reference
3.1.4 element, n—an isolated (totally bounded by void)
practice for measuring groove or tread pattern void areas in a
projection. (F538)
tire-footprint impression. This technique is usable by any
3.1.5 footprint area, [L ], n—the gross contact area of a tire
laboratory without special equipment although more sophisti-
that is loaded (under stated conditions) against a smooth flat
cated procedures are also commonly employed, such as optical
surface. (F538)
or video camera processes.
3.1.6 groove, n—a void that is relatively narrow compared
1.3 The values stated in SI units are to be regarded as the
to its length. (F538)
standard. The values given in parentheses are for information
3.1.7 groove (void) area, [L ], n—that portion of tire foot-
only.
print area that is not contacted by ribs or elements.
1.4 This standard does not purport to address all of the
3.1.8 groove (void) area fraction, [nd], n—the ratio of the
safety concerns, if any, associated with its use. It is the
groove (void) area to the footprint area of a tire. (F538)
responsibility of the user of this standard to establish appro-
3.1.9 lateral groove, n—a groove that has its long dimension
priate safety and health practices and determine the applica-
oriented at direction non-parallel to the tire circumferential
bility of regulatory limitations prior to use.
centerline; it most frequently opens into a void at both ends.
(F538)
2. Referenced Documents
2 3.1.10 notch, n—a groove smaller in both width and length
2.1 ASTM Standards:
than a lateral groove, that contains one closed end. (F538)
F538 Terminology Relating to the Characteristics and Per-
3.1.10.1 Discussion—For the purpose of this practice, it is
formance of Tires
wider than 1 mm and more than 25 % as deep as a groove in
the same tire (see Fig. 1).
3. Terminology
3.1.11 projection, n—a pavement contacting area of the
3.1 Definitions:
tread band, bounded by void. (F538)
3.1.1 circumferential line, n—on a tire, any real or imagi-
3.1.12 rib, n—a continuous circumferential projection.
nary circle on the surface of a tire, lying in a plane that is
(F538)
perpendicular to the spin axis. (F538)
3.1.13 rib or element area, [L ], n—that area within the
outer periphery of a tire footprint that is contacted by ribs or
elements.
This practice is under the jurisdiction of ASTM Committee F09 on Tires and is
3.1.14 sipe, n—a molded or cut rectangular void that is
the direct responsibility of Subcommittee F09.30 on Laboratory (Non-Vehicular)
Testing.
substantially narrower than the major grooves or voids. (F538)
Current edition approved Jan. 1, 2016. Published February 2016. Originally
3.1.15 total or gross-contact area, [L ], n—that area encom-
approved in 1984. Last previous edition approved in 2010 as F870 – 94 (2010).
passed by the outer periphery of a tire footprint.
DOI: 10.1520/F0870-94R16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.1.16 void, n—a volume (in the tread band) defined by the
contact ASTM Customer Service at service@astm.org. 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
F870 − 94 (2016)
FIG. 1 Schematic Diagrams Kerf (Sipe) and Notch
FIG. 2 Footprint Zones A, B and C
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 describes the necessary measurements made on
the footprint impression, or copies thereof, to permit a calcu-
lation of the groove-area fraction. Supplementary footprint
width and length measurements may also be made.
4.2 The groove-area fraction is calculated from measure-
ments 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
A
FIG. 3 Definition of Shoulder Edge in Patterns That Do Not Con-
total or gross-footprint area in this region. The gross area can
tain a Solid Shoulder
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
tire load (within 62 %). The machine shall have a smooth, flat,
pavement, normally contains geometric tread pattern elements
hard base upon which the tire is loaded. The rate of loading
that are defined by grooves or voids. These are employed to
shall be such that no tire bounce or oscillation occurs upon
confer appropriate traction properties to the tire, mainly on wet
cessation of loading. Rates of vertical travel of 2 mm/s (4.7
or snow-covered roads.
in./min) or less in the loading operation are satisfactory.
5.2 One characteristic feature of tire tread patterns that is
7.2 Ink Pad—A soft, inked pad of sufficient area to apply ink
important for both traction and tire wear behavior is the percent
to the surface of the tread. An office foam-rubber stamp pad
or “fractional” groove area. The groove-area fraction is calcu-
used with stamp-pad ink is recommended. The pad shall be
lated with respect to the total or gross contact area.
inked so that the foam-pad material is fully saturated.
However, avoid excess ink, which frequently causes edge
6. Interferences
distortions of the footprint impression.
6.1 Certain difficulties may be encountered in making
7.3 Footprint-Impression Paper—Paper of a size sufficient
groove-area fraction and footprint dimensional measurements.
to accommodate the inked footprint. The paper shall be smooth
These are principally concerned with decisions on what to
and of sufficient thickness (or weight) to prevent surface
include as void area. Tires are designed with a multitude of
buckling or crimping during the tire load process. The ink
geometrical features that show up on the footprint as a void
should not smear or penetrate beyond the geometrically defined
area. Section 3 addresses these problems. Subjective judge-
rib areas due to capillary or other similar action.
ments as to what to include cannot be avoided, and where such
decisions are believed to be relevant, it is necessary that
NOTE 1—The use of pressure-sensitive paper is permissible if the user
sufficient explanation be made in the final report. can demonstrate that the impression is clearly defined and equivalent to an
inked print.
6.2 One typical difficulty is illustrated in Fig. 2 in defining
the outside shoulder edge of the footprint in tires that do not
8. Procedure
have a continuous well-defined shoulder rib edge. The total
8.1 Tire Footprint Impression:
area should be obtained by defining the edge of the print as
shown in Fig. 3.
7. Apparatus 3
A Carter foam-rubber stamp pad No. 2 (80 by 150 mm (3 by 6 in.)) and Carter
stamp pad ink No. 414, manufactured by Dennison Carter Ink Company, 321
7.1 Tire Loading Machine—A machine or fixture that is
Fortune Blvd., Milford, MA 01752, have been found to be satisfactory.
capable of holding a rim-mounted tire vertically at normal 4
Recording chart paper X-Y-1101-SPI, manufactured by Graphic Controls
inflation pressures and that is capable of applying a specified Corp., 189 Van Rensselaer St., Buffalo, NY 14201, has been found to be satisfactory.
F870 − 94 (2016)
8.1.1 Mount the tire on the test rim specified by the Tire and 8.1.8 Rotate the center of the inked zone to the midpoint of
Rim Association Yearbook and inflate to the inflation pressure the footprint-loading position and, with the paper held in place
(see 8.1.2) for the load selected. Inspect the tread surface for at its edges by tape, load the tire to the load corresponding to
irregularities, such as mold vent protrusions, and remove any the inflation pressure being used. If the maximum inflation
found. pressure is being used, then use the maximum load that is
shown on the sidewall of the tire. For loads at inflation
8.1.2 In the absence of any specific recommendations for
inflation pressure, inflate to the maximum inflation pressure pressures other than maximum, consult the Tire and Rim
Association Year Book. Allow a few seconds to elapse and
which is shown on the sidewall of the tire.
unload the tire.
8.1.3 For tires with numerous mold-vent projections, buff
8.1.9 Inspect the footprint for clean, sharp rib-projection
the tread surface lightly with a power-belt sander using fine
imp
...
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 2010) F870 − 94 (Reapproved 2016)
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 health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
F538 Terminology Relating to the 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.
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 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)
3.1.10 notch, n—a groove smaller in both width and length than a lateral groove, that contains one closed end. (F538)
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 Dec. 1, 2010Jan. 1, 2016. Published March 2011February 2016. Originally approved in 1984. Last previous edition approved in 20052010 as
F870 – 94 (2005).(2010). DOI: 10.1520/F0870-94R10.10.1520/F0870-94R16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
3.1.10.1 Discussion—
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F870 − 94 (2016)
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).
3.1.11 projection, n—a pavement contacting area of the tread band, bounded by void. (F538)
3.1.12 rib, n—a continuous circumferential projection. (F538)
3.1.13 rib or element area, [L ],n—that area within the outer periphery of a tire footprint that is contacted by ribs or elements.
3.1.14 sipe, n—a molded or cut rectangular void that is substantially narrower than the major grooves or voids. (F538)
3.1.15 total or gross-contact area, [L ],n—that area encompassed by the outer periphery of a tire footprint.
3.1.16 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 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
A
gross-footprint area 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.
A Carter foam-rubber stamp pad No. 2 (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 been found to be satisfactory.
FIG. 1 Schematic Diagrams Kerf (Sipe) and Notch
F870 − 94 (2016)
FIG. 2 Footprint Zones A, B and C
FIG. 3 Definition of Shoulder Edge in Patterns That Do Not Contain a Solid Shoulder
7.3 Footprint-Impression Paper—Paper of a size sufficient to accommodate the inked footprint. The paper shall be smooth and
of sufficient thickness (or weight) 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 Yearbook 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 due to buffing.
8.1.4 In the absence of power equipment, remove the mold-vent projections or flash, or both, by applying a slight extension to
the projection by hand and carefully cutting the excess from the tread face with a small,
...
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