1993 GMC Safari Owner's Manual - Page 287

If youeverreplaceyourtireswiththosenothavinga TPC Specnumber, makesurethey are thesamesize,loadrange,speedratingandconstruction type(bias,bias-beltedorradial)asyouroriginaltires. I A Mixing tires could cause you to lose controlwhiledriving. I you mix f tires of different sizes or types (like radial and bias-belted tires) the vehicle may not handleproperly,and you could have a crash.Be sure to use the same size and type ti'res on all wheels. It's all right to drivewithyourcompactspare,though.Itwasdevelopedfor limited use on your vehicle. Uniform Tire Quality Grading Thefollowinginformationrelatestothesystemdeveloped bytheUnited StatesNationalHighwayTrafficSafetyAdministrationwhichgradestiresby to treadwear,tractionandtemperatureperformance.(Thisappliesonly vehiclessold in theUnitedStates.) Treadwear Thetreadweargradeisacomparativeratingbasedonthewearrate of the tire whentestedundercontrolledconditionsonaspecifiedgovernmenttest 150 wouldwearoneandahalf (1-112) course. For example,atiregraded times as wellonthegovernmentcourseas i2 tiregraded 100. Therelative performance of tiresdependsuponthe actual1 conditions of theiruse, to variationsin however,andmaydepartsignificantlyfromthenormdue drivinghabits,servicepracticesanddifferencesinroadcharacteristicsand climate. Traction-A, By C Thetractiongrades,fromhighest to lowesttire: A, B, and C. Theyrepresent the tire's ability to stoponwetpavementasmeasuredundercontrolled of asphaltandconcrete. A conditions on specified government test surfaces tire marked C mayhavepoortractionperformance, to this tire isbasedonbraking Warning:Thetractiongradeassigned (straight-ahead)tractiontestsanddoesnotincludecornering(turning)traction. Temperature--A, B, C Thetemperaturegradesare A (thehighest), B, and C, representingthetire's resistancetothegeneration of heatand its abilitytodissipateheatwhen tested under controlled conditions on a specified indoor laboratory test wheel. Sustainedhightemperaturecancausethematerial of thetire to degenerate andreduce tire life, andexcessivetemperaturecanleadtosuddentire 6-49