ASTM F870-94(2005)

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Designation: F870 – 94 (Reapproved 2005)
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 3.1.3 developed footprint width, [L], n—the maximum lat-
eral dimension of a tire footprint under stated conditions of
1.1 This practice covers a technique for measuring the
measurement. (F538)
groove or void area of a tire tread pattern. The void area is
3.1.4 element, n—an isolated (totally bounded by void)
measured on the inked impression of a tire tread statically
projection. (F538)
loaded against heavyweight paper on a load platen.
3.1.5 footprint area, [L ], n—the gross contact area of a tire
1.2 This procedure is intended to serve as a reference
that is loaded (under stated conditions) against a smooth flat
practice for measuring groove or tread pattern void areas in a
surface. (F538)
tire-footprint impression. This technique is usable by any
3.1.6 groove, n—a void that is relatively narrow compared
laboratory without special equipment although more sophisti-
to its length. (F538)
catedproceduresarealsocommonlyemployed,suchasoptical
3.1.7 groove (void) area, [L ], n—that portion of tire foot-
or video camera processes.
print area that is not contacted by ribs or elements.
1.3 The values stated in SI units are to be regarded as the
3.1.8 groove (void) area fraction, [nd], n—the ratio of the
standard. The values given in parentheses are for information
groove (void) area to the footprint area of a tire. (F538)
only.
3.1.9 lateral groove, n—a groove that has its long dimen-
1.4 This standard does not purport to address all of the
sion oriented at direction non-parallel to the tire circumferen-
safety concerns, if any, associated with its use. It is the
tial centerline; it most frequently opens into a void at both
responsibility of the user of this standard to establish appro-
ends. (F538)
priate safety and health practices and determine the applica-
3.1.10 notch, n—a groove smaller in both width and length
bility of regulatory limitations prior to use.
than a lateral groove, that contains one closed end. (F538)
2. Referenced Documents 3.1.10.1 Discussion—For the purpose of this practice, it is
wider than 1 mm and more than 25% as deep as a groove in
2.1 ASTM Standards:
the same tire (see Fig. 1).
F538 Terminology Relating to the Characteristics and Per-
3.1.11 projection, n—a pavement contacting area of the
formance of Tires
tread band, bounded by void. (F538)
3. Terminology
3.1.12 rib, n—a continuous circumferential projection.
(F538)
3.1 Definitions:
3.1.13 rib or element area, [L ], n—that area within the
3.1.1 circumferential line, n—on a tire, any real or imagi-
outer periphery of a tire footprint that is contacted by ribs or
nary circle on the surface of a tire, lying in a plane that is
elements.
perpendicular to the spin axis. (F538)
3.1.14 sipe, n—a molded or cut rectangular void that is
3.1.2 developed footprint length, [L], n—the maximum
substantially narrower than the major grooves or voids.
footprint dimension in the circumferential direction of the tire,
(F538)
under stated conditions of measurement.
3.1.15 total or gross-contact area,[L ], n—thatareaencom-
passed by the outer periphery of a tire footprint.
This practice is under the jurisdiction ofASTM Committee F09 onTires and is
3.1.16 void, n—a volume (in the tread band) defined by the
the direct responsibility of Subcommittee F09.30 on Laboratory (Non-Vehicular)
lack of rubber; the depth dimension of this volume may vary
Testing.
Current edition approved June 1, 2005. Published June 2005. Originally from point to point in (on) the tread band. (F538)
approvedin1984.Lastpreviouseditionapprovedin2000asF870–94(2000).DOI:
10.1520/F0870-94R05.
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
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the ASTM website.
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F870 – 94 (2005)
FIG. 1 Schematic Diagrams Kerf (Sipe) and Notch
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.
FIG. 3 Definition of Shoulder Edge in Patterns That Do Not
Paragraph 8.2 describes the necessary measurements made on
Contain a Solid Shoulder
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.
the outside shoulder edge of the footprint in tires that do not
4.2 The groove-area fraction is calculated from measure-
have a continuous well-defined shoulder rib edge. The total
ments in the central 60% region of the footprint. This central
area should be obtained by defining the edge of the print as
60% region (calculated from footprint length dimensions) is
shown in Fig. 3.
used to avoid the ambiguities and subjective judgements in
precisely defining the “ends” of a footprint. The groove area
7. Apparatus
fraction, f ,istheratioofthegroove-voidfootprintareatothe
A
7.1 Tire Loading Machine—A machine or fixture that is
total or gross-footprint area in this region. The gross area can
capable of holding a rim-mounted tire vertically at normal
be obtained by direct measurement of this rectangular area.
inflation pressures and that is capable of applying a specified
tireload(within 62%).Themachineshallhaveasmooth,flat,
5. Significance and Use
hard base upon which the tire is loaded. The rate of loading
5.1 The tread of a tire, the annular band that contacts the
shall be such that no tire bounce or oscillation occurs upon
pavement, normally contains geometric tread pattern elements
cessation of loading. Rates of vertical travel of 2 mm/s (4.7
that are defined by grooves or voids. These are employed to
in./min) or less in the loading operation are satisfactory.
conferappropriatetractionpropertiestothetire,mainlyonwet
7.2 Ink Pad—A soft, inked pad of sufficient area to apply
or snow-covered roads.
inktothesurfaceofthetread.Anofficefoam-rubberstamppad
5.2 One characteristic feature of tire tread patterns that is
used with stamp-pad ink is recommended. The pad shall be
importantforbothtractionandtirewearbehavioristhepercent
inked so that the foam-pad material is fully saturated. How-
or “fractional” groove area. The groove-area fraction is calcu-
ever, avoid excess ink, which frequently causes edge distor-
lated with respect to the total or gross contact area.
tions of the footprint impression.
7.3 Footprint-Impression Paper—Paper of a size sufficient
6. Interferences
toaccommodatetheinkedfootprint.Thepapershallbesmooth
6.1 Certain difficulties may be encountered in making
and of sufficient thickness (or weight) to prevent surface
groove-area fraction and footprint dimensional measurements. 4
buckling or crimping during the tire load process. The ink
These are principally concerned with decisions on what to
shouldnotsmearorpenetratebeyondthegeometricallydefined
include as void area. Tires are designed with a multitude of
rib areas due to capillary or other similar action.
geometrical features that show up on the footprint as a void
NOTE 1—The use of pressure-sensitive paper is permissible if the user
area. Section 3 addresses these problems. Subjective judge-
candemonstratethattheimpressionisclearlydefinedandequivalenttoan
mentsastowhattoincludecannotbeavoided,andwheresuch
inked print.
decisions are believed to be relevant, it is necessary that
sufficient explanation be made in the final report.
8. Procedure
6.2 One typical difficulty is illustrated in Fig. 2 in defining
8.1 Tire Footprint Impression:
8.1.1 MountthetireonthetestrimspecifiedbytheTireand
RimAssociationYearbook andinflatetotheinflationpressure
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
Fortune Blvd., Milford, MA 01752, have been found to be satisfactory.
Recording chart paper X-Y-1101-SPI, manufactured by Graphic Controls
Corp.,189VanRensselaerSt.,Buffalo,NY14201,hasbeenfoundtobesatisfactory.
T and RA Yearbook (current edition), available from the Tire and Rim
FIG. 2 Footprint Zones A, B and C Association, 175 Montrose West Ave., Copley, OH 44321.
F870 – 94 (2005)
(see 8.1.2) for the load selected. Inspect the tread surface for pressures other than maximum, consult the Tire and Rim
irregularities, such as mold vent protrusions, and remove any Association Year Book. Allow a few seconds to elapse and
found. unload the tire.
8.1.2 In the absence of any specific recommendations for 8.1.9 Inspect the footprint for clean, sharp rib-projection
inflation pressure, inflate to the maximum inflation pressure impressions and a good rib versus groove contrast, that is, rib
which is shown on the sidewall of the tire. areas that are sufficiently black. Reink and reload the tire if a
8.1.3 For tires with numerous mold-vent projections, buff good footprint is not obtained. Mark the footprint with appro-
the tread su
...