Steering, Suspension and Brakes
Steering, Suspension and Brakes
This domain tests wheel alignment angles, steering geometry, suspension types, hydraulic braking and ABS. You need to relate tyre wear patterns and handling complaints to measurable geometry and hydraulic faults.
Core rules
- Camber is the inward or outward tilt of the wheel; caster is the steering-axis tilt and affects straight-line stability and returnability; toe is the difference in distance between the fronts and rears of the tyres.
- Incorrect toe usually causes feathered edge wear; excessive camber causes one-sided wear; incorrect caster causes pull or poor return.
- Hydraulic pressure = force ÷ area. A larger caliper piston area increases clamping force for the same line pressure.
- Brake fluid is hygroscopic; moisture lowers boiling point and can cause a spongy pedal or fade.
- ABS modulates pressure to prevent wheel lock; a wheel-speed sensor fault can disable ABS and stability control.
Worked example
A brake pedal applies 200 N to a master cylinder with an area of 2 cm². Pressure = 200 ÷ 2 = 100 N/cm². A caliper piston has an area of 20 cm², so force at the caliper = 100 × 20 = 2,000 N. Pressure is transmitted equally, but force depends on area. This is why a larger caliper piston or a smaller master cylinder increases braking force, while pedal travel may increase.
Traps
- Setting toe without centring the steering wheel.
- Diagnosing a pull as a brake fault when caster or tyre conicity is the cause.
- Mixing DOT brake fluids or using fluid from an opened, old container.
- Forgetting to check tyre pressures before alignment.
- Assuming a hard pedal means air in the system; a hard pedal often indicates a booster or hydraulic restriction fault.