Designation:F1650−98(Reapproved2014)´1StandardPracticeforEvaluatingTireTractionPerformanceDataUnderVaryingTestConditions1ThisstandardisissuedunderthefixeddesignationF1650;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.ε1NOTE—EditoriallycorrectedSubsectionX2.4inApril2014.INTRODUCTIONTiretractiontestingprogramsatprovinggroundsorotherexteriortestsitesareoftenextendedoveraperiodofdaysorweeks.Duringthistimeperiodtestconditionsmaychangeduetoanumberofvaryingfactors,forexample,temperature,rainorsnowfall,surfacetexture,waterdepth,andwindvelocityanddirection.Iftireperformancecomparisonsaretobemadeoveranypartofthetestprogram(ortheentireprogram)wherethesetestconditionvariationsareknownorsuspectedtoaffectperformance,thepotentialinfluenceofthesevariationsmustbeconsideredinanyfinalevaluationoftractionperformance.1.Scope1.1Thispracticecoverstherequiredproceduresforexam-iningsequentialcontroltiredataforanyvariationduetochangingtestconditions.Suchvariationsmayinfluenceabso-luteandalsocomparativeperformanceofcandidatetires,astheyaretestedoveranyshortorextendedtimeperiod.Thevariationsaddressedinthispracticearesystematicorbiasvariationsandnotrandomvariations.SeeAppendixX1foradditionaldetails.1.1.1Twotypesofvariationmayoccur:timeortestsequence“trendvariations,”eitherlinearorcurvilinear,andthelesscommontransientorabruptshiftvariations.Ifanyobservedvariationsaredeclaredtobestatisticallysignificant,thecalculationproceduresaregiventocorrectfortheinfluenceofthesevariations.ThisapproachisaddressedinMethodA.1.2Insometestingprograms,apolicyisadoptedtocorrectallcandidatetractiontestdatavalueswithouttheapplicationofastatisticalroutinetodetermineifasignificanttrendorshiftisobserved.ThisoptionispartofthispracticeandisaddressedinMethodB.1.3Theissueofrejectingoutlierdatapointsortestvalu...
