Why does a vehicle need a suspension system?

Roads are rarely perfectly flat. The vehicle needs a system to compensate for imperfections in the road which interact with the wheels­, causing shocks. All forces have both direction and magnitude. An imperfection in the road causes the vehicle’s wheel to move vertically at 90° to the road’s surface. The magnitude of the force depends on whether the wheel is striking a rock or a tiny stone.

Without a structure to compensate these forces, all of the wheel’s vertical energy would be transferred to the vehicle’s chassis, causing continuous vibrations and pressure on the contact points between the chassis and the wheels. No structure could last for a long time under these conditions. The wheels would lose contact with the road when driving over any imperfection and driving would be bumpy, uncomfortable and dangerous.

Suspension system types

Suspension systems can be dependent or independent. Most cars have different types of suspension for the front and rear, although this is not always the case. A few common types of suspension systems are introduced here.

Type 1 – Solid axle (dependent)

- This type of suspension is only used on rear wheels. The wheels are connected by a solid bar under the car, supported by springs and shock absorbers.

- This system is commonly used as rear suspension in commercial or light commercial vehicles, pick-ups and 4-wheel drive vehicles.

Type 2 – Double wishbone arm (independent)

Double wishbone arm suspension, usually installed in passenger cars, uses two wishbone-shaped arms to fix the wheel. Each wishbone is mounted to the frame in two places and the spindle in one place. A shock absorber and a coil spring absorb vibrations and carry the vertical load.

The advantages of double wishbone arm suspensions are:

- more control over the camber angle of the wheel, leading to better cornering characteristics and more even wear on tyres
- less roll and sway
- a more consistent steering feel

Type 3 – MacPherson strut suspension (independent)

The MacPherson strut combines a shock absorber and a coil spring into a single unit. This creates a lighter, more compact suspension system that is commonly used on both front and rear wheels.

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