Automobile Engineering: Chassis, Transmission, Braking, Steering and Suspension
This domain tests the layout and function of the vehicle as a mechanical system - how power reaches the road, how the vehicle stops, and how it is steered and carried.
Chassis and transmission
- A ladder frame carries body and load in commercial vehicles; monocoque (unibody) is common in cars. The clutch is normally a single-dry-plate friction type; pedal free play of roughly 20–30 mm prevents slip and release-bearing wear.
- A constant-mesh gearbox with synchromesh engages gears without double declutching. Gear ratio = driven teeth ÷ driving teeth, so a low gear has a numerically high ratio and multiplies torque.
- A propeller shaft with universal joints feeds the differential, whose crown wheel and pinion give the final drive; the differential lets the two wheels turn at different speeds in a turn.
Braking
- Hydraulic braking uses a tandem master cylinder for split-circuit safety. Discs resist fade better than drums because they cool in the open air. ABS modulates pressure to hold wheel slip near the optimum instead of locking.
Steering
- Ackermann geometry makes the inner wheel turn more sharply than the outer. Camber is wheel tilt in front view, caster is kingpin tilt in side view, toe-in offsets rolling splay, and kingpin inclination gives self-centring.
Suspension
- Leaf springs suit heavy loads; MacPherson struts and double wishbones suit cars; an anti-roll bar controls body roll; the shock absorber damps spring oscillation rather than carrying weight.
Worked example
Wheelbase 2.6 m, track 1.5 m, inner wheel angle 30°. Approximate outer turning radius = L ÷ tan δ + half track = 2.6 ÷ 0.577 + 0.75 = 4.50 + 0.75 = 5.25 m from the turn centre.
Traps
- Swapping camber and caster, or claiming a differential equalises wheel speeds (it does the opposite).
- Inverting the gear ratio, and treating the shock absorber as a load-carrying spring.