Steering, suspension, wheels and tyres
Steering, suspension, wheels and tyres
This domain tests alignment angles, steering geometry, suspension inspection, wheel balance and tyre diagnosis.
Core rules
- Camber is vertical tilt; caster is steering-axis tilt; toe is the difference front-to-rear of the wheel planes. Toe-in is usually specified in mm or degrees and is the main wear angle.
- Check ride height and tyre pressures before alignment; a bent strut or worn ball joint makes alignment meaningless.
- Wheel balance: static imbalance gives hop; dynamic imbalance gives shimmy. Radial runout limit is typically under 1.5 mm at the tyre tread.
- Tyre wear: both edges worn means underinflation; centre worn means overinflation; one edge worn means camber; feathering means toe. Diagonal wear suggests worn suspension.
- Suspension: bounce test, check for leaks, torn boots, broken springs and play in joints with the wheel unloaded.
Worked example
A car pulls right and the front tyres show feathered edges. Thrust angle is +0.5°, front toe is +4 mm total against a specification of +1 mm. Correct the rear thrust angle first; otherwise the front toe will be set crooked to compensate. After rear adjustment, set front toe to specification with the steering wheel centred and the suspension at normal ride height.
Traps
- Aligning a car with uneven tyre pressure or a loaded boot.
- Confusing static and dynamic balance.
- Setting toe without centring the steering wheel, causing the wheel to sit off-centre.
- Reusing a tyre with a sidewall bulge or exposed cords.