ASE A4 Suspension and SteeringWheel Alignment Diagnosis, Adjustment, and RepairMedium
A vehicle comes into the shop for an alignment check. The alignment machine shows that the front left caster is +3.5 degrees and the front right caster is +2.0 degrees. The manufacturer's specification for caster is +3.0 degrees ±0.5 degrees. The vehicle is reported to pull to the right. Which of the following is the MOST likely cause of the pull?
- AInsufficient positive caster on the front left wheel.
- BExcessive positive caster on the front right wheel.
- CInsufficient positive caster on the front right wheel.
- DExcessive positive caster on the front left wheel.
Show answer & explanationAnswer & explanation
Correct answer: C. Insufficient positive caster on the front right wheel.
A vehicle will pull to the side with less positive caster (or more negative caster). The front right wheel has +2.0 degrees of caster, which is at the lower end of the specification and significantly less positive than the front left's +3.5 degrees, causing a pull to the right.
Why the other options are wrong
- A. Insufficient positive caster on the front left would cause a pull to the left, not the right.
- B. Excessive positive caster on the right would cause a pull to the left, not the right.
- D. Excessive positive caster on the left would cause a pull to the left, not the right.
Caster and Steering Pull
Caster is the forward or rearward tilt of the steering axis when viewed from the side. It influences steering stability and returnability, and unequal caster can cause a vehicle to pull.
- Positive caster: top of steering axis tilts rearward.
- Negative caster: top of steering axis tilts forward.
- Vehicle pulls to the side with less positive caster.
- Caster helps maintain straight-line stability.
Memory trick: Less positive caster lets the wheel 'fall back' and pull you to that side.