Steering and Suspension
This domain tests steering geometry, steering mechanisms and the suspension parts that support the vehicle and absorb road shocks.
Steering
- Rack-and-pinion steering converts steering-wheel rotation into sideways movement of the track rods.
- Steering ratio = steering-wheel angle ÷ road-wheel angle. A higher ratio gives easier effort but slower response.
- Camber is the inward or outward tilt of the wheel top when viewed from the front.
- Castor is the backward or forward tilt of the steering axis.
- Toe-in is the difference between the front and rear edges of the same axle's wheels.
- Kingpin inclination helps self-centring.
Suspension
- Springs support the vehicle; shock absorbers damp spring oscillation.
- Leaf springs, coil springs, torsion bars and MacPherson struts are common types.
- An anti-roll bar reduces body roll in corners.
- Unsprung mass is the mass not carried by the springs, such as the axle and wheels.
Worked example
A driver turns the steering wheel 360° and the road wheel moves 30°. Steering ratio = 360 ÷ 30 = 12:1. The reasoning is to divide the input angle by the output angle. A 12:1 ratio means the driver turns twelve degrees for every one degree at the road wheel.
Traps
- Confusing camber with castor. Camber tilts the wheel; castor tilts the steering axis.
- Measuring toe at the front and rear of the vehicle instead of across the same axle.
- Saying shock absorbers carry the load; springs do that.
- Treating a higher steering ratio as faster steering.