SUSPENSION 38 6.10 WHEELS AND TYRES Wheels and tyres assembly is an important part in the vehicle; it has effect on performance of the vehicle. It is responsible to transfer the required road feel to the driver and passengers. Hence it is required to follow correct workshop practices. A) TYRE INSPECTION Inspect the tyre for the following and replace if found. a) Bulge on threads and side walls. b) Cuts, cracks, abnormal, excessive, and Ununiform tyre wear. B) REPLACEMENT OF TYRES: When replacement is necessary, the original equipment type tyre should be used. Replacement tyres should be of the same size, load range, and construction as those originally on the vehicle. Use of any other size or type tyre may affect ride, handling, speedometer/ odometer calibration, vehicle ground clearance and tyre clearance to the body chassis. It is recommended that new tyres be installed in pairs on the same axle. If necessary to replace only one tyre, it should be paired with the tyre having the most tread, to equalize braking traction. Also do not mix different types of tyres (viz. radial, bias etc) on the same vehicle, because it badly affects the handling of the vehicle. C) REPLACEMENT OF WHEELS: Wheels must be replaced if 1) They are bent, 2) Dented, 3) have excessive lateral or radial run out, 4) Air leak through welds, 5) Have elongated bolt holes, 6) If wheel bolts will not stay tight, or 7) If they are heavily rusted. Wheels with greater run out than specification may cause vibrations. Replacement wheels must be equivalent to the original equipment wheels in load capacity, diameter, rim with offset and mounting configuration. A wheel of improper Size or type may affect wheel and bearing life, break cooling, speedometer/odometer calibration, vehicle ground clearance, and tyre clearance to body and chassis. 6.10.1 HOW TO MEASURE WHEEL RUNOUT: To measure wheel run out, it is necessary to use an accurate dial indicator. The tyre may be on or off the wheel. The wheel should be installed on a wheel balancer for proper measurement. Take measurements of both lateral run out and radial run out at both inside and outside of the rim flange. With the dial indicator set in place securely, turn the wheel on full revolution slowly and record every reading of the indicator. fig When the measured run out exceeds the specification and correction by the balancer adjustment is impossible, replace the wheel. If the reading is affected by welding, paint or scratch, it should be ignored. Radial Run out limit Lateral Run out limit Steel wheel /alloy wheel 1.14 mm (0.045 in) 1.4 mm (0.055 in) MATCHED TYRES AND WHEELS: Tyres and wheels are match mounted at the assembly plant. This means that the radially stiffest part of the tyre or “high spot” marked in RED on tyre is matched to the smallest radius or “low spot” of the steel wheel rim. In case of alloy rims valve is to be matched with YELLOW spot on the tyre. The YELLOW spot is an indication of low point of static imbalance of tyres. This is done to provide the smoothest possible ride. The color spots on the tyres are originally marked by paint dot on the out board sidewall. This paint dot will eventually get wash off the tyre.
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