ASE A4 Suspension and SteeringWheels and Tires Diagnosis and RepairMedium
A technician is performing a pre-balance inspection on a tire and wheel assembly. Before mounting the assembly on the balancer, they notice excessive runout on the wheel rim. Which of the following is the MOST appropriate next step?
- AMount the assembly on the balancer and attempt to balance it.
- BRotate the tire 180 degrees on the wheel and recheck runout.
- CInspect the wheel for damage and replace if runout exceeds specifications.
- DReplace the tire, then balance the assembly.
Show answer & explanationAnswer & explanation
Correct answer: C. Inspect the wheel for damage and replace if runout exceeds specifications.
Excessive wheel runout will prevent proper balancing and can cause vibrations. The wheel itself must be inspected for damage and replaced if its runout is beyond manufacturer specifications, as balancing cannot correct a bent or out-of-round wheel.
Why the other options are wrong
- A. Balancing a wheel with excessive runout is futile; it will not correct the underlying issue and will result in a poorly balanced assembly.
- B. While rotating the tire on the wheel (match mounting) can sometimes reduce total runout, it's typically done for tire-related runout or to optimize a good wheel/tire combination, not to fix excessive wheel runout itself. The primary concern here is the wheel's integrity.
- D. Excessive runout is a wheel issue, not typically a tire issue. Replacing the tire would not resolve the problem with the wheel.
Wheel Runout
The deviation of a wheel's rim from a perfectly circular shape (radial runout) or a perfectly flat plane (lateral runout).
- Measured in thousandths of an inch or millimeters.
- Excessive runout causes vibration and cannot be corrected by balancing.
- Can be caused by impacts, manufacturing defects, or corrosion.
Memory trick: Bad wheel runout? Don't balance, replace!