Chassis, Steering, Suspension, and Braking
Chassis, Steering, Suspension, and Braking
This domain tests alignment angles, suspension and steering inspection, hydraulic brake principles, and ABS operation. Expect angle identification, wear-pattern analysis, and force calculations.
Core rules
- Camber is vertical tire tilt; caster is steering-axis tilt; toe is the difference between front and rear tire edges. Total toe equals left plus right.
- Tire wear patterns matter: both inner edges suggest toe-out or negative camber; centre wear suggests overinflation; cupping suggests worn dampers or imbalance.
- Common suspension types include MacPherson strut, double wishbone, and torsion beam. Tighten rubber bushings at ride height.
- Rack-and-pinion steering may use electric power assistance. Check tie-rod play and reset the steering angle sensor after alignment.
- Brake hydraulic pressure = force / area. Pedal ratio multiplies driver force. Disc brakes self-adjust; drum brakes may need adjustment.
- ABS uses wheel-speed sensors; a dirty sensor can set a DTC without a hydraulic fault.
Worked example
A 200 N pedal force with a 4:1 pedal ratio gives 800 N at the master cylinder. Master piston area is 5 cm squared, so pressure = 800 / 5 = 160 N/cm squared. A caliper piston area of 50 cm squared gives clamp force = 160 x 50 = 8,000 N. Reasoning: pressure is equal throughout the hydraulic system; force scales with piston area.
Traps
- Swapping camber and caster definitions.
- Adding toe values incorrectly instead of using total toe.
- Mixing DOT 5 silicone fluid with DOT 3 or DOT 4.
- Torquing suspension bushings at full droop rather than ride height.
- Diagnosing ABS hydraulic failure before checking wheel-speed sensor condition.