ASE A4 Suspension and SteeringWheel Alignment Diagnosis, Adjustment, and RepairHard
A technician is performing an alignment on a vehicle and observes that the front left Steering Axis Inclination (SAI) is 12.0 degrees and the front right SAI is 10.5 degrees. The specification is 11.0 degrees +/- 0.5 degrees. All other alignment angles are within specification. This difference typically indicates a problem with which of the following?
- AA bent steering knuckle or strut.
- BIncorrect caster adjustment.
- CExcessive positive camber.
- DUneven tire pressure on the front wheels.
Show answer & explanationAnswer & explanation
Correct answer: A. A bent steering knuckle or strut.
SAI is a non-adjustable angle, determined by the design of the steering knuckle and strut/spindle assembly. A significant difference in SAI from side to side, especially when other angles are in spec, strongly suggests a bent or damaged component like the steering knuckle, strut, or lower control arm mounting point. SAI is measured from the true vertical and is directly related to the physical components.
Why the other options are wrong
- B. Caster and SAI are independent angles, though they both relate to the steering axis. Incorrect caster adjustment would not directly cause a SAI split.
- C. Camber is an adjustable angle that can be corrected, but it does not directly cause an SAI split. While a bent component might affect both, SAI being out of spec points more directly to structural damage.
- D. Uneven tire pressure primarily affects camber and toe, not SAI.
SAI Discrepancy Diagnosis
Steering Axis Inclination (SAI) is a non-adjustable angle. A significant difference in SAI between the left and right sides typically indicates a bent or damaged component in the steering or suspension system.
- SAI is a fixed, non-adjustable angle.
- Determined by the vehicle's design (knuckle, strut).
- Split SAI often points to structural damage from impact.
Memory trick: SAI's fixed, a split's a clue, component damage, often new.