1993 GMC Suburban Owner's Manual - Page 320

If youeverreplaceyourtireswiththosenothavingaTPCSpecnumber, makesuretheyarethesamesize, load range,speedrating and construction type(bias,bias-beltedorradial) as youroriginaltires. Uniform Tire Thefollowinginformationrelatestothesystemdeveloped by the United StatesNationalHighwayTrafficSafetyAdministrationwhichgradestiresby treadwear,tractionandtemperatureperformance.(Thisappliesonly to vehicles sold in theUnitedStates.) Treadwear Thetreadweargrade is acomparativeratingbased on thewearrateof the tirewhentestedundercontrolledconditions on a specified government test (1 1/2) course.Forexample, a tiregraded 150 wouldwearoneandahalf timesaswellonthegovernmentcourse as atiregraded 100. Therelative performance oftiresdependsupontheactualconditionsoftheiruse, however,andmaydepartsignificantlyfromthenormduetovariations in drivinghabits,servicepracticesanddifferences in roadcharacteristics and climate. Traetiowr-A, B, C Thetractiongrades,fromhighesttolowestare: A, B, andC.Theyrepresent the tire's ability to stoponwetpavement as measuredundercontrolled conditions on specifiedgovernmenttestsurfaces of asphalt and concrete. A tire marked C mayhavepoortractionperformance. Warning:Thetractiongradeassigned to thistire is basedonbraking (straight-ahead)tractiontestsanddoesnotincludecornering(turning)traction. T@mpeaafwae-A, €, Ic Thetemperaturegradesare A (thehighest), B, and C, representingthetire's resistance to the generation of heat and its ability to dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustainedhightemperaturecancausethematerial of thetire to degenerate and reducetirelife,andexcessivetemperaturecan lead to suddentire failure.ThegradeCcorresponds to a level ofperformancewhichall passengercartiresmustmeetundertheFederalMotorVehicleSafety 6-54