Wheels and Tires: Testing and Inspection
Inspection and VerificationWarning:
^ A vehicle equipped with a Traction-Lok differential will always have both wheels driving. If, while the vehicle is being repaired, only one wheel is raised off the floor and the rear axle is driven by the engine, the wheel on the floor can drive the vehicle off the stand or jack. Be sure both rear wheels are off the floor. Failure to follow these instructions may result in personal injury.
Warning:
^ Never run the engine with one wheel off the ground, for example, when changing a tire. The wheel(s) resting on the ground could cause the vehicle to move. Failure to follow these instructions may result in personal injury.
Warning:
^ Do not balance the wheels and tires while they are still mounted on the vehicle. Possible tire disintegration or differential failure can result, causing serious injury and extensive component damage. Use off-vehicle wheel and tire balancer only. Failure to follow these instructions may result in personal injury.
Be sure to follow the warnings when carrying out inspection and verification.
Road Test
Verify the customer concern by carrying out a road test on a smooth road. If any vibrations are apparent, refer to SUSPENSION; NOISE, VIBRATION AND HARSHNESS (NVH).
To maximize tire performance, inspect for signs of incorrect inflation and uneven wear, which can indicate a need for balancing, rotation, or a suspension alignment. Correct tire pressure and driving techniques have an important influence on tire life. Heavy cornering, excessively rapid acceleration and unnecessary sharp braking increase tire wear.
Replacement tires should follow the recommended:
^ tire sizes
^ speed rating
^ load range
^ tire construction type
Use of any other tire size or type may seriously affect:
^ ride
^ handling
^ speedometer/odometer calibration
^ vehicle ground clearance
^ tire clearance between the body and chassis
^ wheel bearing life
^ brake cooling
Wheels need to be replaced when:
^ bent
^ dented
^ cracked
^ heavily corroded
^ leaking
^ they have elongated wheel hub bolt holes
^ they have excessive lateral or radial runout
Wheel and tire assemblies are attached by five wheel nuts
It is mandatory to use only the tire sizes recommended on the tire chart attached to the vehicle. Larger or smaller tires can damage the vehicle, affect driveability, and require changing the speedometer calibration. Make sure wheel size and offsets match those recommended for the tire in use.
1. Inspect for signs of uneven wear that can indicate a need for balancing, rotation, suspension alignment, or damaged steering components.
2. Check tires for:
1. cuts
2. stone bruises
3. abrasions
4. blisters
5. embedded objects
3. Tread wear indicators are molded into the bottom of the tread grooves. Install a new tire when the indicator bar becomes visible.
Match Mounting Tires
Match mounting is a technique used to reduce radial runout. Excessive runout is a source of vibration, shimmy and poor handling concerns. Use the following steps to reduce radial runout:
1. Mark the wheel at the same point as the mark previously made when measuring the tire runout.
2. Dismount the tire and remount it 180 degrees on the wheel so the original mark on the tire is opposite the mark on the wheel.
3. Inflate the tire to specification.
4. Measure the radial runout with Radial Runout Gauge at the center of the tread face: If the radial runout is reduced to acceptable guidelines, the tire can be used: If the radial runout remains excessive, check the wheel runout.
Tire Lead Diagnosis
Lead is the deviation of the vehicle from a straight path on a level road with no pressure on the steering wheel. Lead can be caused by:
^ incorrect wheel alignment
^ dragging brakes
^ incorrect/uneven tire pressure
^ defective tires
If defective tires are suspected in a lead condition, use the following steps to determine the defective tire:
1. Rotate the two front tires.
2. Road test the vehicle: If the vehicle leads to the opposite direction, one of the front tires is at fault.
3. Rotate the two front tires back to their original position.
4. Rotate one of the front tires with its corresponding rear tire on the same side of the vehicle.
5. Road test the vehicle: If the lead is corrected, install a new rear tire: If the lead remains, install a new front tire on the opposite side of the vehicle.
Component Tests
Tire and Wheel Runout
Before checking runout, and to avoid false readings caused by temporary flat spots in the tires, check runout only after the vehicle has been driven far enough to warm the tires.
Excessive radial and lateral runout of a wheel and tire assembly can cause roughness, vibration, wheel tramp, tire wear, and steering wheel tremor.
The extent of the runout is measured with a radial runout gauge. All measurements are made on the vehicle with the tires inflated to recommended inflation pressures.
Tire Runout
Measure radial and lateral runout at the positions shown in the illustration. Runout should not exceed specifications.
Wheel Runout
Measure radial and lateral wheel runout at the positions shown on the illustration. Runout should not exceed specifications. Note that the tire has been removed.