Wheels and Tires: Testing and Inspection
DIAGNOSIS AND TESTING - TIRE AND WHEEL VIBRATIONTire and wheel imbalance, runout and force variation can cause vehicles to exhibit steering wheel vibration.
VISUAL INSPECTION
Visual inspection of the vehicle is recommended prior to road testing or performing any other procedure. Raise vehicle on a suitable hoist.
Inspect for the following:
- Verify correct (OEM) wheel and tire, as well as correct wheel weights. Aluminum wheels require unique wheel weights. They are designed to fit the contour of the wheel (Fig. 1).
- Inspect tires and wheels for damage, mud packing and unusual wear; correct as necessary.
- Check and adjust tire air pressure to the pressure listed on the label attached to the rear face of the driver's door.
ROAD TEST
Road test vehicle on a smooth road for a least five miles to warm tires (remove any flat spots). Lightly place hands on steering wheel at the 10:00 and 2:00 positions while slowly sweeping up and down from 90 to 110 km/h (55 to 70 mph) where legal speed limits allow.
Observe the steering wheel for:
- Visual Nibble (oscillation: clockwise/counterclockwise, usually due to tire imbalance)
- Visual Buzziness (high frequency, rapid vibration up and down)
To rule out vibrations due to brakes or powertrain:
- Lightly apply brakes at speed; if vibration occurs or is enhanced, vibration is likely due to causes other than tire and wheel assemblies.
- Shift transmission into neutral while vibration is occurring; if vibration is eliminated, vibration is likely due to causes other than tire and wheel assemblies.
For tire and wheel assembly vibrations, continue with this diagnosis and testing procedure.
TIRE AND WHEEL BALANCE
1. Balance the tire and wheel assemblies as necessary following the wheel balancer manufacturer's instructions and using the information listed in Standard Procedure - Tire And Wheel Balance.
2. Road test the vehicle for at least 5 miles, following the format described in Road Test.
3. If the vibration persists, continue with this diagnosis and testing procedure.
TIRE AND WHEEL RUNOUT/MATCH MOUNTING
1. System Radial Runout. This on-the-vehicle system check will measure the radial runout including the hub, wheel and tire.
a) Raise vehicle so tires clear floor.
b) Apply masking tape around the circumference of the tire in the locations to be measured (Fig. 2). Do not overlap the tape.
c) Check system runout using Dial Indicator Set, Special Tool C-3339A with 25-W wheel, or equivalent. Place the end of the indicator against each taped area (one at a time) (Fig. 2) and rotate the tire and wheel. System radial runout should not exceed 0.76 mm (0.030 inch) with no tread "dips" or "steps." Tread "dips" and "steps" can be identified by spikes of the dial indicator gauge.
- Tread "dips"; Rapid decrease then increase in dial indicator reading over 101.6 mm (4.0 inch) of tread circumference.
- Tread "steps"; Rapid decrease or increase in dial indicator reading over 101.6 mm (4.0 inch) of tread circumference.
d) If system runout is excessive, re-index the tire and wheel assembly on the hub. Remove assembly from vehicle and install it back on the hub two studs over from original mounting position. If re-indexing the tire and wheel assembly corrects or reduces system runout, check hub runout and repair as necessary.
e) If system runout is still excessive, continue with this diagnosis and testing procedure.
2. Tire and Wheel Assembly Radial Runout. This radial runout check is performed with the tire and wheel assembly off the vehicle.
a) Remove tire and wheel assembly from vehicle and install it on a suitable wheel balances.
b) Check system runout using Dial Indicator Set, Special Tool C-3339A with 25-W wheel, or equivalent. Place the end of the indicator against each taped area (one at a time) (Fig. 2) and rotate the tire and wheel. Radial runout should not exceed 0.76 mm (0.030 inch) with no tread "dips" or "steps." Tread "dips" and "steps" can be identified by spikes of the dial indicator gauge.
c) If runout exceeds limits, mark the original location of the tire on the wheel at the valve stem (Fig. 3). Also, mark the tire and wheel to indicate the original high spot of the assembly and record the runout measurement.
d) If runout exceeds limits, the tire will need to be dismounted from the wheel to verify wheel vs. tire contribution. Refer to Wheel Runout.
3. Lateral Runout. Lateral runout for the vehicle system as well as the tire and wheel assembly should be less than 0.76 mm (0.030 inch). The same procedure and theory described for radial runout can also be applied to identify and reduce lateral runout.
4. Wheel Runout. This runout check is performed as follows:
a) Dismount the tire from the wheel.
b) Mount the wheel back on the wheel balances.
c) Measure radial runout of the wheel at the tire bead seat (Fig. 4). Runout should not exceed 0.254 mm (0.010 inch) for aluminum wheels and 0.508 mm (0.020 inch) for steel wheels. Replace the wheel if it exceeds the limit.
d) Measure lateral runout of the wheel at the tire bead seat (Fig. 5). Runout should not exceed 0.762 mm (0.030 inch) for all wheels. Replace the wheel if it exceeds the limit.
5. Match Mounting. If the wheel runout is within specifications, tire and wheel assembly runout can be improved by re-indexing (match mounting) the tire to the wheel as described.
a) Remount the tire on the rim 180 degrees from its original location (Fig. 6). Ensure the tire bead is properly seated.
b) Re-measure the total runout. Mark the tire at the high spot and record the measurement.
If runout is still excessive, perform the following:
- If the new high spot is within 102 mm (4.0 inch) of the first high spot on the tire, replace the tire.
- If the new high spot is within 102 mm (4.0 inch) of the first high spot on the wheel, the wheel may be out of specification. Refer to Wheel Runout above.
- If the new high spot is NOT within 102 mm (4.0 inch) of either high spot, draw an arrow on the tread from new high spot toward the original (Fig. 7). Break down the tire and remount it 90 degrees on rim in that direction, then re-measure runout. This will normally reduce the runout to an acceptable amount.
6. Once back together, road test the vehicle for at least 5 miles, following the format described in Road Test. If vibration persists, and all components tested are within specification, the tires may have an excessive radial force condition. Radial force variation can only be checked as indicated. If this equipment is not available, consult with the tire manufacturer.
RADIAL FORCE VARIATION
Radial Force Variation can be checked using the Hunter GSP 9700 Vibration Control System (Wheel Balancer) or equivalent, if available. This type of equipment helps to correct ride disturbances by reducing the radial force variation of an assembly through re-indexing of the tire to wheel.
The equipment manufacturer or DaimlerChrysler Corporation may supply reference values as guidelines. Radial force measurements above the reference value may not always result in a ride disturbance, nor do they automatically mean the assembly components are out of specification. Do not replace components based on radial force values alone. Balancing, runout diagnosis, re-indexing, and subjective road testing must be performed as outlined in diagnosis and testing procedure.
Use the Radial Force equipment to identify suspect assemblies and minimize the radial forces. After all suspect assemblies are optimized, reinstall the assemblies and road test the vehicle. If a disturbance still exists and all other vibration diagnostic procedures have been completed, replace one tire or one wheel at a time, starting with the assembly having the highest force variation. Be sure to minimize each new assembly. Road test the vehicle following each replacement. Continue this process until the disturbance is resolved.
NOTE: When using Radial Force equipment, it is critically important to set proper tire inflation pressure and ensure centering of the wheel on the equipment spindle.
RADIAL FORCE VARIATION REFERENCE VALUES