Transmission, Steering and Suspension Systems
What this domain tests
Power flow from clutch to wheels, gear ratios, differential action, steering geometry and suspension types. Numerical ratio questions and alignment-angle definitions are common.
Core rules and concepts
- The clutch transmits torque by friction. It slips when lining wear or weak springs reduce clamp force; it drags when it fails to release fully.
- Gear ratio = driven teeth / driving teeth. Overall ratio = gearbox ratio × final-drive ratio.
- The differential lets inner and outer wheels turn at different speeds in a turn while still delivering drive.
- Steering geometry: camber is wheel lean viewed from the front; caster is the steering-axis tilt that gives self-centring; toe is the difference between front and rear of the wheels; KPI/SAI is the kingpin inclination.
- Ackermann steering makes the inner wheel steer a larger angle than the outer wheel.
- Springs carry load; dampers control spring oscillation. Common layouts: MacPherson strut, double wishbone, leaf spring and torsion bar.
Worked example
Engine speed 3000 rpm, first gear 3.5:1, final drive 4.0:1, tyre circumference 2.0 m. Wheel speed = 3000 / (3.5 × 4.0) = 214.3 rpm. Road speed = 214.3 × 2.0 = 428.6 m/min = 25.7 km/h. Reason: divide by both reductions, then convert wheel revolutions to distance per minute.
Traps that cost marks
Saying a differential forces both wheels to turn at the same speed; confusing caster with camber; mixing toe units (mm and degrees); condemning a damper from a bounce test alone.