Learner Zone

Suspension

Suspension is the system of tyres, tyre air, springs, shock absorbers and linkages that connect a vehicle to its wheels and allows relative motion between the two. Suspension systems must support road holding, handling and ride quality, which are at all odds with each other.

There are various ways to attach the wheels of the car so they can move up and down on their springs and dampers with as little change as possible in the distance between adjacent wheels or in the angle of the tyres to the road. The front wheels must be free to pivot on their steering swivels. The driven wheels, whether front or rear, must also be free to rotate with the drive shafts.

independent

Instead of sharing a common axle, each wheel on a car with independent suspension is independently attached to the body or subframe. Different spring combinations may be used. When driven wheels are independently suspended, the differential is fixed to the frame and drives the wheels by jointed drive shafts.

There are five types of suspension system in common use.

Double wishbones are used mostly at the front. There are two wishbones, one above the other, that keep the wheel upright as it rises and falls.

MacPherson-strut suspension can be used at both front and rear. The wheel hub is fixed rigidly to an upright, telescopic, tubular strut which has its top end anchored to the frame or to a reinforced wing. On front wheels, the whole strut swivels to allow steering. Pivoted arms extend inward and forward to the frame in order to keep the wheel upright and resist accelerating and braking forces.

A trailing arm is attached to the wheel hub at one end, and extends forward to a pivot on the frame. The arm may be broadened into a V shape with two pivots, either side by side or with the inner pivot slightly behind the front one. Trailing arms are usually found at the rear only.

A leading arm, used only at the front, is the opposite of a trailing arm, with the wheel in front of the pivot.

Swing axles may be used at the front or rear. The system is like a beam axle cut in half and attached to pivots on the frame. Usually the half-axle is broadened into a V with front and rear pivots to keep it from twisting.

To restrain cars from rolling/leaning an anti-roll bar is used. It is a torsion bar crossing the car through two pivots on opposite sides of the frame. Outside the pivots the bar bends back and one end is attached to each wheel, usually through one or two flexible rubber bushes. When one wheel moves up it pulls one end of the bar and the other end pulls the other wheel, keeping the car level.