Steering and Suspension
This domain covers steering geometry, rack-and-pinion and recirculating-ball systems, power steering, suspension types, springs, dampers and wheel alignment. The exam tests alignment angles and how each affects handling and tyre wear.
Core rules
Camber is the inward or outward tilt of the wheel viewed from the front; negative camber tilts the top inward. Caster is the fore-aft tilt of the steering axis; positive caster improves straight-line stability and self-centring. Toe is the difference in track between the front and rear of the tyres; incorrect toe causes feathering and scrub. Steering axis inclination and included angle help diagnose bent components. Ackermann geometry makes the inner wheel steer a smaller radius than the outer. Power steering may be hydraulic, electric or electro-hydraulic; air in a hydraulic system causes whine and heavy steering.
Worked example
A toe measurement uses two points 400 mm apart on the wheel rim. The front track is 3 mm narrower than the rear, so total toe-in is 3 mm. The angle is arctan(3 / 400) = 0.43 degrees total, or about 0.21 degrees per wheel. If the specification is 0.10 ± 0.10 degrees per wheel, the setting is out of tolerance and must be adjusted at the tie rods.
Traps
Confusing toe-in with toe-out; adjusting camber to cure a pull caused by a dragging brake; measuring alignment with a loaded or damaged suspension; and assuming caster changes tyre shoulder wear. Negative camber wears the inner shoulder; positive camber wears the outer shoulder.