ASTM F870-94(2010)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:F870 −94(Reapproved 2010)
Standard Practice for
Tread Footprints of Passenger Car Tires Groove Area
Fraction and Dimensional Measurements
ThisstandardisissuedunderthefixeddesignationF870;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
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
catedproceduresarealsocommonlyemployed,suchasoptical
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—agroovethathasitslongdimension
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)
F538Terminology 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 ofASTM 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 Dec. 1, 2010. Published March 2011. Originally
3.1.15 total or gross-contact area,[L ],n—thatareaencom-
approved in 1984. Last previous edition approved in 2005 as F870–94 (2005).
DOI: 10.1520/F0870-94R10. passed by the outer periphery of a tire footprint.
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 (2010)
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 ,istheratioofthegroove-voidfootprintareatothe
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
tireload(within 62%).Themachineshallhaveasmooth,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
conferappropriatetractionpropertiestothetire,mainlyonwet
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—Asoft,inkedpadofsufficientareatoapplyink
importantforbothtractionandtirewearbehavioristhepercent
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.
toaccommodatetheinkedfootprint.Thepapershallbesmooth
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
shouldnotsmearorpenetratebeyondthegeometricallydefined
area. Section 3 addresses these problems. Subjective judge-
rib areas due to capillary or other similar action.
mentsastowhattoincludecannotbeavoided,andwheresuch
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. candemonstratethattheimpressionisclearlydefinedandequivalenttoan
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
ACarter 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
Recording chart paper X-Y-1101-SPI, manufactured by Graphic Controls
inflation pressures and that is capable of applying a specified Corp.,189VanRensselaerSt.,Buffalo,NY14201,hasbeenfoundtobesatisfactory.
F870−94 (2010)
8.1.1 MountthetireonthetestrimspecifiedbytheTireand 8.1.8 Rotate the center of the inked zone to the midpoint of
RimAssociationYearbook andinflatetotheinflationpressure 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
8.1.2 In the absence of any specific recommendations for shown on the sidewall of the tire. For loads at inflation
pressures other than maximum, consult the Tire and Rim
inflation pressure, inflate to the maximum inflation pressure
which is shown on the sidewall of the tire. Association Year Book. Allow a few seconds to elapse and
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
impressions and a good rib versus g
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