ASTM F870-94(2000)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: F 870 – 94 (Reapproval 2000)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope measurement. (F 538)
3.1.4 element, n—an isolated (totally bounded by void)
1.1 This practice covers a technique for measuring the
projection. (F 538)
groove or void area of a tire tread pattern. The void area is
3.1.5 footprint area, [ L ], n— the gross contact area of a
measured on the inked impression of a tire tread statically
tire that is loaded (under stated conditions) against a smooth
loaded against heavyweight paper on a load platen.
flat surface. (F 538)
1.2 This procedure is intended to serve as a reference
3.1.6 groove, n—a void that is relatively narrow compared
practice for measuring groove or tread pattern void areas in a
to its length. (F 538)
tire-footprint impression. This technique is usable by any
3.1.7 groove (void) area, [ L ], n— that portion of tire
laboratory without special equipment although more sophisti-
footprint area which is not contacted by ribs or elements.
catedproceduresarealsocommonlyemployed,suchasoptical
3.1.8 groove (void) area fraction, [nd], n—the ratio of the
or video camera processes.
groove (void) area to the footprint area of a tire. (F 538)
1.3 The values stated in SI units are to be regarded as the
3.1.9 lateral groove, n—a groove that has its long dimen-
standard. The values given in parentheses are for information
sion oriented at direction non-parallel to the tire circumferen-
only.
tial centerline; it most frequently opens into a void at both
1.4 This standard does not purport to address all of the
ends. (F 538)
safety concerns, if any, associated with its use. It is the
3.1.10 notch, n—a groove smaller in both width and length
responsibility of the user of this standard to establish appro-
than a lateral groove, that contains one closed end. (F 538)
priate safety and health practices and determine the applica-
3.1.10.1 Discussion—For the purpose of this practice, it is
bility of regulatory limitations prior to use.
widerthan1mmandmorethan25percentasdeepasagroove
2. Referenced Documents in the same tire (see Fig. 1).
3.1.11 projection, n—a pavement contacting area of the
2.1 ASTM Standards:
tread band, bounded by void. (F 538)
F538 Terminology Relating to the Characteristics and Per-
3.1.12 rib, n—a continuous circumferential projection.
formance of Tires
(F 538)
3. Terminology
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
3.1 Definitions:
elements.
3.1.1 circumferential line, n— on a tire, any real or imagi-
3.1.14 sipe, n—a molded or cut rectangular void that is
nary circle on the surface of a tire, lying in a plane that is
substantially narrower than the major grooves or voids.
perpendicular to the spin axis. (F 538)
(F 538)
3.1.2 developed footprint length, [L], n—the maximum
3.1.15 total or gross-contact area,[L ], n—thatareaencom-
footprint dimension in the circumferential direction of the tire,
passed by the outer periphery of a tire footprint.
under stated conditions of measurement.
3.1.16 void, n—a volume (in the tread band) defined by the
3.1.3 developed footprint width, [L], n—the maximum lat-
lack of rubber; the depth dimension of this volume may vary
eral dimension of a tire footprint under stated conditions of
from point to point in (on) the tread band. (F 538)
4. Summary of Practice
This practice is under the jurisdiction ofASTM Committee F-9 onTires and is
the direct responsibility of Subcommittee F09.30 on Laboratory (Non-Vehicular)
4.1 This practice is divided into two parts. Paragraph 8.1
Testing.
provides a procedure to obtain a tire footprint impression.
Current edition approved Feb. 15, 1994. Published April 1994. Originally
Paragraph 8.2 describes the necessary measurements made on
published as F870–84. Last previous edition F870–89.
Annual Book of ASTM Standards, Vol 09.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F 870 – 94 (Reapproval 2000)
FIG. 1 Schematic Diagrams Kerf (Sipe) and Notch
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-
FIG. 3 Definition of Shoulder Edge in Patterns That Do Not
Contain a Solid Shoulder
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 7. Apparatus
precisely defining the “ends” of a footprint. The groove area
7.1 Tire Loading Machine—A machine or fixture that is
fraction, f ,istheratioofthegroove-voidfootprintareatothe
A
capable of holding a rim-mounted tire vertically at normal
total or gross-footprint area in this region. The gross area can
inflation pressures and that is capable of applying a specified
be obtained by direct measurement of this rectangular area.
tireload(within 62%).Themachineshallhaveasmooth,flat,
hard base upon which the tire is loaded. The rate of loading
5. Significance and Use
shall be such that no tire bounce or oscillation occurs upon
5.1 The tread of a tire, the annular band that contacts the
cessation of loading. Rates of vertical travel of 2 mm/s (4.7
pavement, normally contains geometric tread pattern elements
in./min) or less in the loading operation are satisfactory.
that are defined by grooves or voids. These are employed to
7.2 Ink Pad—A soft, inked pad of sufficient area to apply
conferappropriatetractionpropertiestothetire,mainlyonwet
inktothesurfaceofthetread.Anofficefoam-rubberstamppad
or snow covered roads.
used with stamp-pad ink is recommended. The pad shall be
5.2 One characteristic feature of tire tread patterns that is
inked so that the foam-pad material is fully saturated. How-
importantforbothtractionandtirewearbehavioristhepercent
ever,avoidexcessinkwhichfrequentlycausesedgedistortions
or “fractional” groove area. The groove-area fraction is calcu-
of the footprint impression.
lated with respect to the total or gross contact area.
7.3 Footprint-Impression Paper—Paper of a size sufficient
toaccommodatetheinkedfootprint.Thepapershallbesmooth
6. Interferences
and of sufficient thickness (or weight) to prevent surface
6.1 Certain difficulties may be encountered in making buckling or crimping during the tire load process. The ink
shouldnotsmearorpenetratebeyondthegeometricallydefined
groove-area fraction and footprint dimensional measurements.
rib areas due to capillary or other similar action.
These are principally concerned with decisions on what to
include as void area. Tires are designed with a multitude of
NOTE 1—The use of pressure-sensitive paper is permissible if the user
geometrical features that show up on the footprint as a void
candemonstratethattheimpressionisclearlydefinedandequivalenttoan
area. Section 3 addresses these problems. Subjective judge-
inked print.
mentsastowhattoincludecannotbeavoided,andwheresuch
8. Procedure
decisions are believed to be relevant, it is necessary that
sufficient explanation be made in the final report. 8.1 Tire Footprint Impression:
6.2 One typical difficulty is illustrated in Fig. 2 in defining
8.1.1 MountthetireonthetestrimspecifiedbytheTireand
the outside shoulder edge of the footprint in tires that do not RimAssociationYearbook andinflatetotheinflationpressure
have a continuous well-defined shoulder rib edge. The total
(see 8.1.2) for the load selected. Inspect the tread surface for
area should be obtained by defining the edge of the print as irregularities, such as mold vent protrusions, and remove any
shown in Fig. 3.
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.
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.
F 870 – 94 (Reapproval 2000)
8.1.3 Fortireswithnumerousmold-ventprojectionsbuffthe good footprint is not obtained. Mark the footprint with appro-
tread surface lightly with a power-belt sander using fine priate identifying data.
abrasive paper. Do this with the inflated tire and rim assembly
8.1.10 Repeat for all selected footprint zones. Allow all
mounted on a power-driven spindle rotating at 10 to 15 r/min.
footprintstothoroughlydrybeforemakingcopiesformeasure-
Apply light pressure when buffing, always moving the buffer
ments.
laterallybackandforth.Aremovalof0.
...