Steering, Suspension and Wheels
This domain tests how the vehicle is steered, how road shocks are absorbed, and how wheels, tyres and alignment angles affect wear and safety.
Steering system
The steering wheel turns a steering gear - rack and pinion in cars, worm and roller or recirculating ball in heavier vehicles. Steering ratio is steering wheel rotation compared with road wheel rotation; a higher ratio reduces effort but slows the response. Wheel alignment angles include camber (top of wheel leaning in or out), caster (steering axis tilt giving self-centring and stability), king pin or steering axis inclination, and toe-in or toe-out. Ackermann geometry makes the inner wheel turn more sharply than the outer on a bend. Correct toe setting reduces tyre scrub and feathering, which is typical of too much toe.
Suspension
Suspension locates the wheels, carries the load and isolates the body from road irregularities. Springs may be leaf (multi-leaf, solid and simple, used on trucks), coil, torsion bar or air. A telescopic hydraulic double-acting shock absorber damps spring oscillations; a worn shock gives floating, bounce and uneven tyre wear. Independent suspension, such as the MacPherson strut or double wishbone, lets each wheel move separately and gives better ride and roadholding.
Wheels and tyres
Rims may be well-based, drop-centre or flat-based. Tyres are cross-ply or radial; radials have more flexible sidewalls, run cooler, last longer and reduce rolling resistance. A marking such as 155/70 R13 means section width 155 mm, aspect ratio 70 percent, radial construction, 13-inch rim diameter. Wheel balance prevents vibration at speed.
Worked example
A car wears both edges of the front tyres. Reasoning: both edges wearing together indicates under-inflation, not a camber error or excessive toe. Checking and correcting the cold inflation pressure against the specification is the first step; if pressure is correct, check for sustained heavy loading or a mismatched tyre.
Traps that cost marks
Mixing up camber and caster; saying radial tyres use a stiffer cross-ply construction; confusing under-inflation edge wear with over-inflation centre wear; forgetting that toe affects feathering.