Braking, Steering and Suspension Systems
This domain tests hydraulic braking, steering geometry, and suspension action. You should be able to explain Pascal’s law, brake bleeding, wheel alignment angles, and how springs and dampers affect tyre contact.
Core rules
- Hydraulic brakes transmit pressure through fluid. Pressure is force divided by piston area; a larger caliper piston produces greater clamping force for the same line pressure.
- Air in the hydraulic circuit is compressible and causes a spongy pedal; bleeding removes it.
- ABS prevents wheel lock during hard braking by modulating pressure, preserving steering control.
- Steering geometry includes camber (wheel lean from vertical), caster (steering-axis tilt), toe (wheel pointing in or out), and kingpin inclination. Incorrect settings cause uneven tyre wear and poor straight-line stability.
- Suspension springs support load; dampers control oscillation. Worn dampers reduce tyre contact and increase stopping distance.
Worked example
A 200 N pedal force acts on a 20 mm master-cylinder piston. Area = πd²/4 = π(20²)/4 ≈ 314 mm². Pressure = 200 ÷ 314 ≈ 0.637 N/mm² ≈ 6.37 bar. A caliper piston of 40 mm has area ≈ 1,257 mm², so clamping force = 0.637 × 1,257 ≈ 800 N. The reasoning is that pressure is common throughout the fluid, while force depends on each piston’s area.
Traps that cost marks
- Confusing camber with caster; camber is wheel lean, caster is steering-axis tilt.
- Measuring toe with uneven tyre pressures or worn joints.
- Forgetting that a spongy pedal points to air, not necessarily a worn pad.
- Overlooking a seized caliper slide pin when diagnosing brake drag.
- Judging suspension only by bounce; check leakage and tyre wear patterns.