ASE A4 Suspension and SteeringWheels and Tires Diagnosis and RepairMedium
A client complains of a vibration that is felt primarily through the steering wheel at speeds between 50-70 mph. The technician performs a road force balance, and the results show a high road force variation (RFV) of 30 lbs (13.6 kg) on the left front wheel. The maximum allowable RFV for this vehicle is 15 lbs (6.8 kg). What is the MOST appropriate next action?
- AAdd more balance weights to the wheel to compensate for the high RFV.
- BRotate the tire on the rim (match-mounting) to reduce the RFV.
- CPerform a static balance instead of a road force balance.
- DReplace the tire immediately due to a manufacturing defect.
Show answer & explanationAnswer & explanation
Correct answer: B. Rotate the tire on the rim (match-mounting) to reduce the RFV.
High road force variation indicates a stiff spot in the tire or a runout issue. Match-mounting, which involves rotating the tire on the rim relative to the wheel's low spot, is a common and effective technique to minimize RFV by aligning the tire's high spot with the wheel's low spot.
Why the other options are wrong
- A. Adding more balance weights only corrects static/dynamic imbalance, not road force variation.
- C. A static balance only addresses weight distribution, not the tire's uniformity or road force variation.
- D. While replacement might be necessary eventually, match-mounting is a standard first step to attempt to correct RFV before condemning the tire.
Road Force Variation (RFV) Correction
Road Force Variation (RFV) measures the change in force exerted by a tire as it rolls under load. High RFV is corrected by match-mounting the tire to the wheel to offset the tire's stiff spot with the wheel's low spot.
- Caused by tire uniformity issues or excessive wheel runout.
- Causes vibrations, especially at highway speeds.
- Match-mounting is the primary correction method.
Memory trick: High Force, Match-Mount to Smooth Course.