Suspension System: Suspension system layouts

Suspension System:

Driven rear suspension layouts

A number of different layouts are used in ”driven” or 'live' axle rear suspension systems.

This driven or 'live' rear axle arrangement consists of: shock absorbers; u-bolts; fixed shackle; rebound clips and swinging shackles.


This arrangement consists of: coil springs; flexible bushes and upper & lower control arms.

This arrangement consists of: coil springs; flexible bushes; panhard rods and upper & lower control arms.

This arrangement consists of: coil springs; flexible bushes; Watts Linkage and upper & lower control arms.

Non-driven rear suspension layouts

A number of different layouts are used in non-driven or 'dead' axle rear suspension systems.

This non-driven or 'dead' axle rear suspension arrangement consists of: coil springs; flexible bushes; panhard rod; forward control arm and rearward control arm.

This arrangement consists of: axle beam; torsion bar; trailing arm; panhard rod; coil springs and strut.

This arrangement consists of: coil spring; strut; trailing link and lateral links.

Independent rear suspension layouts

A number of different layouts are used in independent driven or 'live' axle rear suspension systems.

This independent driven or 'live' rear axle arrangement consists of: coil springs; flexible bushes; CV joints; external drive-shafts and semi-trailing arms.

This arrangement consists of: coil springs; drive shafts; cross member; universal joints and lower suspension link.

This arrangement consists of: coil springs & strut; splined sections; lateral wishbone and external drive shafts.

This independent driven or 'live' axle arrangement can be either front or rear suspension and consists of: torsion bar; upper wishbone; lower wishbone and torsion bar adjustment.

Front suspension layouts

A number of different layouts are used in front suspension systems, incorporating either a driven or 'live' axle; or a non-driven or 'dead' axle.

This independent driven or 'live' axle front suspension arrangement consists of: coil spring; lower wishbone and McPherson strut.

This arrangement consists of: coil spring; strut; tension rod and lower control arm.

This non-driven or 'dead' axle front suspension arrangement consists of: coil springs; lower wishbone and upper wishbone.

This arrangement consists of: coil springs; tension rod; lower control arm and upper wishbone.

Bushes/bushings

Bushes, or bushings, act as bearings at suspension fulcrum points, to allow for movement of the component, while maintaining its alignment.
They can be metallic, or made of rubber, nylon, or urethane.
In commercial vehicles, metallic bushes are commonly used as shackle bushes for leaf springs. Any force applied to the bush acts through it to the body of the vehicle, which results in a harsher ride.
The mounting pin on a metallic bush is usually drilled to allow for lubricating the bushes.
Rubber bushes isolate noise and harshness, and dampen unwanted vibrations. Rubber bonded bushes can be used to mount the steering rack to the vehicle frame. The rubber absorbs small impacts from the suspension action, without transmitting them to the vehicle. Rubber requires no lubrication.
Spring shackle bushes can be molded to form two halves, to fit into each side of the spring eye, on the swinging shackle. With the spring loaded, and the shackle plates tightened, the rubber is compressed in the eye and at the face of the plates. As the spring deflects, the rubber shears without tearing.
Metalastic, or rubber-bonded, bushes are normally used for the front eye of the spring, at the fixed shackle point, and also in control arm applications.
The bush has a steel outer casing and inner sleeve. The rubber medium is bonded to both, to provide flexibility between them. The outer casing is normally pressed into place in the component. Relative movement between the casing and the inner sleeve causes the rubber to shear without tearing.
In control arm applications, particularly at the rear of a vehicle, the rubber arm may be molded with a voided section. This is known as a compliance bush because it allows the unit or component to comply with a controlled amount of movement in the direction of the void.
This movement relative to the vehicle frame, allows compliance or deflection steer of the road wheels when cornering. Since this influences the steering behavior of the vehicle it is very important the voided section is in its correct, relative position.

Arms & linkages

The major components of the suspension system must be firmly located, to withstand the forces that occur in normal operation.
Control arms fasten a component like a rear axle assembly to the vehicle body, while allowing it to move as it needs to.
Similarly, with a steering knuckle.
The arms must be strong enough to withstand the forces due to normal operation, but light enough to minimize the vehicle’s unsprung mass.
The front suspension can have 1, or 2, control arms. Parallel-link front suspensions have 2 control arms.
Vehicles with strut-type front suspension have only 1 arm. It can be a wish-bone shape with 2 fulcrum mounting points, or straight with single fulcrum.
The inner end of the control arm is bushed to the vehicle body, and the outer end uses a ball joint to allow changes in the steering angle for turning.
This rear-wheel-drive vehicle has coil springs in the rear suspension; therefore special provision must be made to locate the axle, laterally and longitudinally.
Trailing arms, or control rods, are used to position the axle longitudinally. They have flexible rubber mountings at each end where they locate on the axle housing, and on the chassis frame.
They would allow the axle to move laterally if it were not restrained. Any such movement has to be controlled to keep correct alignment with the front wheels, and the vehicle frame.
This suspension system uses angled, upper-control rods, to limit lateral movement of the rear axle, during cornering.
They also absorb the torque reaction forces, which limits rear axle wind-up during accelerating, and braking.
A panhard rod may be used to restrict lateral movement of the rear axle during cornering. It has bushes or mountings at each end, where it locates on the axle and frame.
This allows for variations in load, while maintaining correct alignment.
The axle may also be located by a Watts linkage. A lever, mounted on a pivot near the centre of the axle housing, is connected by rods to the frame, on each side of the vehicle.
This maintains the axle in alignment with the frame, while still allowing the suspension to move vertically.