Steering, suspension, wheels and tyres
Steering, suspension, wheels and tyres covers geometry, linkage and springing, plus the marking and inspection of tyres.
Steering geometry
Camber is the inward or outward tilt of the wheel viewed from the front. Caster is the tilt of the steering axis viewed from the side; positive caster gives self-centring. Toe-in or toe-out is the difference in track between front and rear of the wheels. Kingpin inclination and scrub radius affect steering feel and stability. Ackermann geometry lets the inner wheel turn more sharply.
Suspension and tyres
MacPherson struts combine a coil spring and damper; double wishbones, torsion bars and leaf springs are also used. Dampers control spring oscillation, and worn dampers cause tyre cupping. Wheel bearings must have the specified end float or preload.
Worked example. A tyre marked 195/65 R15 91H: width = 195 mm, aspect ratio = 65%, radial construction, rim diameter = 15 in. Sidewall height = 195 × 0.65 = 126.75 mm. Rim diameter in mm = 15 × 25.4 = 381 mm. Overall diameter = 381 + 2 × 126.75 = 634.5 mm. Load index 91 corresponds to 615 kg per tyre at the rated pressure; H is a speed rating of 210 km/h.
Traps
Confusing camber with caster. Setting toe with worn tyres or loose joints. Over-tightening wheel bearings. Mixing radial and cross-ply tyres on the same axle. Ignoring the 1.6 mm tread wear indicator.