WHEELS, RIMS AND TIRESWHEEL AND TIRE BALANCINGFront wheel and tire assemblies must be balanced toprevent wheel vibrating and bounce. While the correctfront wheel alignment is necessary for easy steering andmaximum tire life, the cause of unstable steering canfrequently be traced to improper balance of front wheels.When this condition exists, the wheel and tire assemblyshould be properly balanced.A vulcanized or retreaded tire, or a tire that has a boot init, may cause an unbalanced condition that cannot becorrected by balancing. In such cases the tire should bereplaced before attempting to balance the assembly.Static BalancingA wheel out of balance statically has a tendency tobounce up and down, resulting in rapid tire wear in roundor oblong spots.Static balancing is performed while wheel is stationary byattaching weights to rim flange to offset an oppositeheavy point.Static balancing may be sufficient in some instanceswhere vehicle is operated only at slow speeds, however,dynamic balancing (in motion) balances the wheel andtire assembly statically as well as dynamically, therebyeliminating vibrations and wheel bounce at both low andhigh speeds.A wheel may be perfectly balanced statically (not inmotion) but may still vibrate and bounce at high speedrotation because of its being out of balance dynamically.Dynamic BalancingDynamic balancing is complete wheel balancing of whichstatic balancing is only a part.Dynamic balancing (in motion) takes into considerationthe distribution of weight to be added to the wheel. ThisIs accomplished by rapidly rotating (normal truckoperating speed) the wheel and tire assembly either onthe vehicle or with the wheel assembly removed andplaced on a dynamic balancing machine. Thisdetermines heavy point on wheel.When the amount of weight required to offset a heavypart in a wheel assembly is known, it is sometimesnecessary to attach one-half of the weight to the outsiderim flange and the remaining half to the inside rim flange.With the weight properly distributed on the wheelassembly, the wheel should be in balance both staticallyand dynamically and should rotate free of vibration andbounce at normal truck operating speeds.TIRE CAREProper tire inflation, tire loads, and road speeds areimportant determining factors governing tire mileage,and also affect steering ease and maneuverability. Howmuch these three factors affect tire wear is illustrated inthe paragraphs which follow.INFLATIONTire pressures should be checked at regular andfrequent intervals and the pressures maintained tospecifications. Use an accurate tire pressure gauge andcheck when tires are cool.Over inflated or under inflated tires will reduce the ser-vice life of the tire."Bleeding" of air from hot tires should never be practiced.The pressure will be reduced but an increase intemperature will result as soon as driving continues.LOADSLoading tires beyond their rated capacity is expensivebecause tire mileages are rapidly decreased withoverloads.TIRE MATCHINGDual TiresUse care in matching dual tires. Tires which differ morethan 6.35 mm (1/4") in diameter or 19.05 mm (3/4") Incircumference should not be mounted on the same dualwheel. Should it become necessary to mount two tires ofunequal size on the same dual wheel, place the larger orless worn tire on the outside.Tandem Drive AxlesWhen mounting tires on tandem drive axles follow thesame instructions as specified for dual tires. However,never install the four largest tires on one driving axle andthe four smallest on the other. This method of tiremounting will cause high lubricant temperatures whichmay lead to premature axle failures.CTS-4148APage 22
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