Steering and Suspension Systems
Steering and Suspension Systems
This domain tests steering geometry, steering gear types, suspension layouts and tyre wear diagnosis. Expect questions on camber, caster, toe and the effect of worn shock absorbers.
Core rules
- Steering: rack-and-pinion is common in cars; recirculating-ball steering boxes are used in heavier vehicles. Power steering may be hydraulic or electric (EPS).
- Geometry: camber is the inward or outward tilt of the wheel viewed from the front; caster is the forward or backward tilt of the steering axis viewed from the side; toe is the difference in distance between the front and rear of the front wheels. Kingpin inclination and included angle affect steering return.
- Suspension: McPherson strut, double wishbone, leaf spring (live axle), coil spring, torsion bar. Shock absorbers damp spring oscillation; they do not carry the vehicle's weight.
- Wheel balance and runout cause vibration; alignment causes pull and uneven wear.
- Tyre wear: both edges worn = under-inflation; centre worn = over-inflation; one edge = camber; feathered = toe; cupping = worn dampers or balance.
Worked example
A car pulls to the left and the front tyres show excessive wear on the inner shoulder. The specification is toe-in 2 ± 1 mm, but measurement gives 5 mm. Reasoning: 5 mm is outside tolerance, indicating excessive toe-in; the inner shoulders scrub. The pull suggests a camber or caster difference as well, so check and adjust tyre pressures first, then set toe with the steering centred and the suspension loaded. Adjust both tie rods equally to keep the steering wheel straight, then road-test.
Traps
- Confusing camber with caster.
- Checking alignment with worn tyres, loose ball joints or the wrong tyre pressures.
- Calling a shock absorber a spring.
- Setting toe with the steering wheel off-centre.