Designation:F870−94(Reapproved2010)StandardPracticeforTreadFootprintsofPassengerCarTiresGrooveAreaFractionandDimensionalMeasurements1ThisstandardisissuedunderthefixeddesignationF870;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.1.Scope1.1Thispracticecoversatechniqueformeasuringthegrooveorvoidareaofatiretreadpattern.Thevoidareaismeasuredontheinkedimpressionofatiretreadstaticallyloadedagainstheavyweightpaperonaloadplaten.1.2Thisprocedureisintendedtoserveasareferencepracticeformeasuringgrooveortreadpatternvoidareasinatire-footprintimpression.Thistechniqueisusablebyanylaboratorywithoutspecialequipmentalthoughmoresophisti-catedproceduresarealsocommonlyemployed,suchasopticalorvideocameraprocesses.1.3ThevaluesstatedinSIunitsaretoberegardedasthestandard.Thevaluesgiveninparenthesesareforinformationonly.1.4Thisstandarddoesnotpurporttoaddressallofthesafetyconcerns,ifany,associatedwithitsuse.Itistheresponsibilityoftheuserofthisstandardtoestablishappro-priatesafetyandhealthpracticesanddeterminetheapplica-bilityofregulatorylimitationspriortouse.2.ReferencedDocuments2.1ASTMStandards:2F538TerminologyRelatingtotheCharacteristicsandPer-formanceofTires3.Terminology3.1Definitions:3.1.1circumferentialline,n—onatire,anyrealorimagi-narycircleonthesurfaceofatire,lyinginaplanethatisperpendiculartothespinaxis.(F538)3.1.2developedfootprintlength,[L],n—themaximumfootprintdimensioninthecircumferentialdirectionofthetire,understatedconditionsofmeasurement.3.1.3developedfootprintwidth,[L],n—themaximumlat-eraldimensionofatirefootprintunderstatedconditionsofmeasurement.(F538)3.1.4element,n—anisolated(totallyboundedbyvoid)projection.(F538)3.1.5footprintarea,[L2],n—thegrosscontactareaofatirethatisloaded(understatedconditions)againstasmoothflatsurface.(F538)3.1.6groove,n—avoidthatisrel...
