1、Designation: F 870 94 (Reapproved 2005)Standard Practice forTread Footprints of Passenger Car Tires Groove AreaFraction and Dimensional Measurements1This standard is issued under the fixed designation F 870; the number immediately following the designation indicates the year oforiginal adoption or,
2、in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a technique for measuring thegroove or void area of a tire
3、tread pattern. The void area ismeasured on the inked impression of a tire tread staticallyloaded against heavyweight paper on a load platen.1.2 This procedure is intended to serve as a referencepractice for measuring groove or tread pattern void areas in atire-footprint impression. This technique is
4、 usable by anylaboratory without special equipment although more sophisti-cated procedures are also commonly employed, such as opticalor video camera processes.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standa
5、rd does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 AST
6、M Standards:2F 538 Terminology Relating to the Characteristics and Per-formance of Tires3. Terminology3.1 Definitions:3.1.1 circumferential line, non a tire, any real or imagi-nary circle on the surface of a tire, lying in a plane that isperpendicular to the spin axis. (F 538)3.1.2 developed footpri
7、nt length, L, nthe maximumfootprint dimension in the circumferential direction of the tire,under stated conditions of measurement.3.1.3 developed footprint width, L, nthe maximum lat-eral dimension of a tire footprint under stated conditions ofmeasurement. (F 538)3.1.4 element, nan isolated (totally
8、 bounded by void)projection. (F 538)3.1.5 footprint area, L2, nthe gross contact area of a tirethat is loaded (under stated conditions) against a smooth flatsurface. (F 538)3.1.6 groove, na void that is relatively narrow comparedto its length. (F 538)3.1.7 groove (void) area, L2, nthat portion of ti
9、re foot-print area that is not contacted by ribs or elements.3.1.8 groove (void) area fraction, nd, nthe ratio of thegroove (void) area to the footprint area of a tire. (F 538)3.1.9 lateral groove, na groove that has its long dimen-sion oriented at direction non-parallel to the tire circumferen-tial
10、 centerline; it most frequently opens into a void at bothends. (F 538)3.1.10 notch, na groove smaller in both width and lengththan a lateral groove, that contains one closed end. (F 538)3.1.10.1 DiscussionFor the purpose of this practice, it iswider than 1 mm and more than 25 % as deep as a groove i
11、nthe same tire (see Fig. 1).3.1.11 projection, na pavement contacting area of thetread band, bounded by void. (F 538)3.1.12 rib, na continuous circumferential projection.(F 538)3.1.13 rib or element area, L2, nthat area within theouter periphery of a tire footprint that is contacted by ribs orelemen
12、ts.3.1.14 sipe, na molded or cut rectangular void that issubstantially narrower than the major grooves or voids.(F 538)3.1.15 total or gross-contact area, L2, nthat area encom-passed by the outer periphery of a tire footprint.3.1.16 void, na volume (in the tread band) defined by thelack of rubber; t
13、he depth dimension of this volume may varyfrom point to point in (on) the tread band. (F 538)1This practice is under the jurisdiction ofASTM Committee F09 on Tires and isthe direct responsibility of Subcommittee F09.30 on Laboratory (Non-Vehicular)Testing.Current edition approved June 1, 2005. Publi
14、shed June 2005. Originallyapproved in 1984. Last previous edition approved in 2000 as F 870 94(2000).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards D
15、ocument Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Practice4.1 This practice is divided into two parts. Paragraph 8.1provides a procedure to obtain a tire footprint impression.Paragr
16、aph 8.2 describes the necessary measurements made onthe footprint impression, or copies thereof, to permit a calcu-lation of the groove-area fraction. Supplementary footprintwidth and length measurements may also be made.4.2 The groove-area fraction is calculated from measure-ments in the central 60
17、 % region of the footprint. This central60 % region (calculated from footprint length dimensions) isused to avoid the ambiguities and subjective judgements inprecisely defining the “ends” of a footprint. The groove areafraction, fA, is the ratio of the groove-void footprint area to thetotal or gross
18、-footprint area in this region. The gross area canbe obtained by direct measurement of this rectangular area.5. Significance and Use5.1 The tread of a tire, the annular band that contacts thepavement, normally contains geometric tread pattern elementsthat are defined by grooves or voids. These are e
19、mployed toconfer appropriate traction properties to the tire, mainly on wetor snow-covered roads.5.2 One characteristic feature of tire tread patterns that isimportant for both traction and tire wear behavior is the percentor “fractional” groove area. The groove-area fraction is calcu-lated with res
20、pect to the total or gross contact area.6. Interferences6.1 Certain difficulties may be encountered in makinggroove-area fraction and footprint dimensional measurements.These are principally concerned with decisions on what toinclude as void area. Tires are designed with a multitude ofgeometrical fe
21、atures that show up on the footprint as a voidarea. Section 3 addresses these problems. Subjective judge-ments as to what to include cannot be avoided, and where suchdecisions are believed to be relevant, it is necessary thatsufficient explanation be made in the final report.6.2 One typical difficul
22、ty is illustrated in Fig. 2 in definingthe outside shoulder edge of the footprint in tires that do nothave a continuous well-defined shoulder rib edge. The totalarea should be obtained by defining the edge of the print asshown in Fig. 3.7. Apparatus7.1 Tire Loading MachineA machine or fixture that i
23、scapable of holding a rim-mounted tire vertically at normalinflation pressures and that is capable of applying a specifiedtire load (within 62 %). The machine shall have a smooth, flat,hard base upon which the tire is loaded. The rate of loadingshall be such that no tire bounce or oscillation occurs
24、 uponcessation of loading. Rates of vertical travel of 2 mm/s (4.7in./min) or less in the loading operation are satisfactory.7.2 Ink PadA soft, inked pad of sufficient area to applyink to the surface of the tread.An office foam-rubber stamp padused with stamp-pad ink is recommended.3The pad shall be
25、inked so that the foam-pad material is fully saturated. How-ever, avoid excess ink, which frequently causes edge distor-tions of the footprint impression.7.3 Footprint-Impression PaperPaper of a size sufficientto accommodate the inked footprint. The paper shall be smoothand of sufficient thickness (
26、or weight) to prevent surfacebuckling or crimping during the tire load process.4The inkshould not smear or penetrate beyond the geometrically definedrib areas due to capillary or other similar action.NOTE 1The use of pressure-sensitive paper is permissible if the usercan demonstrate that the impress
27、ion is clearly defined and equivalent to aninked print.8. Procedure8.1 Tire Footprint Impression:8.1.1 Mount the tire on the test rim specified by the Tire andRimAssociation Yearbook5and inflate to the inflation pressure3A Carter foam-rubber stamp pad No. 2 (80 by 150 mm (3 by 6 in.) and Carterstamp
28、 pad ink No. 414, manufactured by Dennison Carter Ink Company, 321Fortune Blvd., Milford, MA 01752, have been found to be satisfactory.4Recording chart paper X-Y-1101-SPI, manufactured by Graphic ControlsCorp., 189 Van Rensselaer St., Buffalo, NY14201, has been found to be satisfactory.5T and RA Yea
29、rbook (current edition), available from the Tire and RimAssociation, 175 Montrose West Ave., Copley, OH 44321.FIG. 1 Schematic Diagrams Kerf (Sipe) and NotchFIG. 2 Footprint Zones A, B and CFIG. 3 Definition of Shoulder Edge in Patterns That Do NotContain a Solid ShoulderF 870 94 (2005)2(see 8.1.2)
30、for the load selected. Inspect the tread surface forirregularities, such as mold vent protrusions, and remove anyfound.8.1.2 In the absence of any specific recommendations forinflation pressure, inflate to the maximum inflation pressurewhich is shown on the sidewall of the tire.8.1.3 For tires with
31、numerous mold-vent projections, buffthe tread surface lightly with a power-belt sander using fineabrasive paper. Do this with the inflated tire and rim assemblymounted on a power-driven spindle rotating at 10 to 15 r/min.Apply light pressure when buffing, always moving the bufferlaterally back and f
32、orth.Aremoval of 0.05 to 0.1 mm (0.002 to0.004 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 themold-vent projections or flash, or both, by applying a slightextension to the projection
33、 by hand and carefully cutting theexcess from the tread face with a small, very sharp knife orpocket nail clippers.8.1.5 Tires frequently contain tread-element dimensionalvariations (size, spacing, pitch, length, etc.) to reduce noisetonality in service use. When such variations exist, it isnecessar
34、y to represent the tire with an average groove or voidarea. A recommended technique is outlined in 8.1.6. However,the recommended selection of three zones as outlined may notadequately achieve this objective, and it may be necessary tomodify the location to obtain a representative set of footprintim
35、pressions.8.1.6 Three zones are recommended for making footprintimpressions. These zones, A, B, and C, are located as follows:8.1.6.1 Zone A, from the DOT serial number side is definedby a plane perpendicular to a line through the center of the axisof rotation and the first letter of the DOT serial
36、number.8.1.6.2 Zone B, is located so that the center of the footprintis spaced 120 clockwise from the footprint center of Zone A.8.1.6.3 Zone C, is located so that the center of the footprintis 240 clockwise (120 counter-clockwise) from the center ofZone A. The footprints shall conform to within 65
37、of thespecified zone-footprint center as specified herein. (See Fig. 2.)8.1.7 Install the mounted tire and rim assembly in theloading machine or fixture. Locate the first footprint zone andposition in an upright orientation. Ink the tread region thor-oughly with firm pressure pad application, over a
38、 circumfer-ential arc of approximately 30 cm. Inspect the inked surface toassure:8.1.7.1 That all rib projections are fully inked and wetted(Note 2).8.1.7.2 That excess inking has not occurred as manifestedby a buildup of ink on the edges of the ribs.NOTE 2To assure thorough wetting of the rubber wi
39、th the ink, it maybe desirable to clean the tread surface with a hydrocarbon solvent (hexane,heptane) prior to inking. Allow the solvent to evaporate.8.1.8 Rotate the center of the inked zone to the midpoint ofthe footprint-loading position and, with the paper held in placeat its edges by tape, load
40、 the tire to the load corresponding tothe inflation pressure being used. If the maximum inflationpressure is being used, then use the maximum load that isshown on the sidewall of the tire. For loads at inflationpressures other than maximum, consult the Tire and RimAssociation Year Book. Allow a few
41、seconds to elapse andunload the tire.8.1.9 Inspect the footprint for clean, sharp rib-projectionimpressions and a good rib versus groove contrast, that is, ribareas that are sufficiently black. Reink and reload the tire if agood footprint is not obtained. Mark the footprint with appro-priate identif
42、ying data.8.1.10 Repeat for all selected footprint zones. Allow allfootprints to thoroughly dry before making copies for measure-ments.8.2 Measurements on the Footprint Impression:8.2.1 Reproduce the original footprints of the three zonesusing a copier that suitably differentiates between contact an
43、dvoid regions and does not cause dimensional variations of thelength and width dimensions greater than 61 %. A photocopyof the original impression is made to eliminate variation ofweight due to inking.8.2.2 A typical footprint is shown in Fig. 4. The central60 % region is obtained as follows:8.2.2.1
44、 Draw footprint “end lines” a and a8 as shown. Thehorizontal position of these is not critical, but they should, inthe subjective judgement of the person doing the analysis,reasonably represent the end of the footprint. In footprints thathave shoulder lengths greater than crown lengths, the shoulder
45、dimensions should be used to locate the end lines.8.2.2.2 Measure dFL, the distance between end lines (174mm in this example), and divide this distance by 5. (For thisexample, this gives 34.8 35). Measure inward 35 mm foreach end line as shown and draw line b and b8. These latter twolines constitute
46、 the ends of the 60 % central region for use inthe footprint measurement.8.2.3 Determine the location of the outside shoulder edgesof the footprint and measure dFW(see Figs. 3-4).8.2.4 Cut out the rectangular 60 % region of the paper-footprint impression and weigh to the nearest 0.005 g. This isthe
47、weight of the paper-footprint impression, WT.8.2.5 With a razor blade or other suitable instrument,accurately cut out the groove or void areas of the 60 % region.Do not include in this any kerfs or sipes, but do cut out anynotches. If kerfs or sipes are of a borderline nature, make aspecial note as
48、to whether they are included or not. Weigh allFIG. 4 Typical Footprint ImpressionF 870 94 (2005)3the cutout groove or void pieces to the nearest 0.005 g. This isthe weight of the groove or void, WV.8.2.6 Determine the nonvoid weight (WNV) by subtractingthe weight WVfrom the weight WT.9. Calculation9
49、.1 Calculate the groove-area fraction, fA, for all threezones, A, B, and C, as follows:fA5WVWV1 WNVCF!(1)where:WV= weight of the void areas of the central footprint(60 %) region, g,WNV= weight of nonvoid (rib, lug areas of footprint)(60 %) region, g,CF = correction factor for image density weight ofnonvoid areas (see Note 3 and Note 9.2), andWT=WV+WNV(CF).NOTE 3The correction factor, CF, is obtained from the weight ormass ratio of nonblackened to blackened areas on the copies produced bythe copier used for the image reproduction. This can
