ASTM_F_870_-_94_2010.pdf

Designation:F87094(Reapproved 2010)Standard Practice forTread Footprints of Passenger Car Tires Groove AreaFraction and Dimensional Measurements1This standard is issued under the fixed designation F870;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()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 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 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 standard 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 ASTM Standards:2F538 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.(F538)3.1.2 developed footprint 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.(F538)3.1.4 element,nan isolated(totally bounded by void)projection.(F538)3.1.5 footprint area,L2,nthe gross contact area of a tirethat is loaded(under stated conditions)against a smooth flatsurface.(F538)3.1.6 groove,na void that is relatively narrow comparedto its length.(F538)3.1.7 groove(void)area,L2,nthat portion of tire 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.(F538)3.1.9 lateral groove,na groove that has its long dimensionoriented at direction non-parallel to the tire circumferentialcenterline;it most frequently opens into a void at both ends.(F538)3.1.10 notch,na groove smaller in both width and lengththan a lateral groove,that contains one closed end.(F538)3.1.10.1 DiscussionFor the purpose of this practice,it iswider than 1 mm and more than 25%as deep as a groove inthe same tire(see Fig.1).3.1.11 projection,na pavement contacting area of thetread band,bounded by void.(F538)3.1.12 rib,na continuous circumferential projection.(F538)3.1.13 rib or element area,L2,nthat area within theouter periphery of a tire footprint that is contacted by ribs orelements.3.1.14 sipe,na molded or cut rectangular void that issubstantially narrower than the major grooves or voids.(F538)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;the depth dimension of this volume may varyfrom point to point in(on)the tread band.(F538)1This practice is under the jurisdiction of ASTM Committee F09 on Tires and isthe direct responsibility of Subcommittee F09.30 on Laboratory(Non-Vehicular)Testing.Current edition approved Dec.1,2010.Published March 2011.Originallyapproved in 1984.Last previous edition approved in 2005 as F870 94(2005).DOI:10.1520/F0870-94R10.2For 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 Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.Summary of Practice4.1 This practice is divided into two parts.Paragraph 8.1provides a procedure to obtain a tire footprint impression.Paragraph 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%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-footp