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What is the suspension/what does it do?
The suspension is a key part of any vehicle. Its job is to cushion the driver and passengers from the bumps and potholes in the road and ensure a smooth, comfortable ride. It increases the friction between the tyres and the road to provide stability in the drive so the driver can control the vehicle, and ensures that tyres wear out evenly.
Getting into the details of the suspension
Where it not for the suspension system, even the smallest of bumps in the road would cause force to travel through the frame of the vehicle and be felt by the driver. In place, a suspension system absorbs the pressure and energy from the speedbumps or holes in the road and allows it to dissipate.
When a vehicle drives over a bump in the road the wheel moves up and down perpendicular to the road. This force is sent through the coil spring, which is a heavy duty metal spring that sits on the wishbone part of the suspension on some vehicles and between the upper and lower control arms in others. These springs are in pairs, two in the front of the vehicle and two in the rear and act like a shock absorber. If one spring breaks, it’s essential to replace its pair at the same time as damage to one will likely indicate damage to the other.
The upper and lower control arms attach to the wheel using ball joints. Their job is to keep the wheels on the ground and prevent tyre hop. They do this by allowing the wheel to move freely up and down and in line with the vehicle’s body. Should any of these be damaged, you may notice your tyres wearing down unevenly. You may also notice a popping or clicking noise if the ball joints are worn.
As well as the coil springs absorbing the shock of any road imperfections, there is also a pair of anti-roll bars. These attach to the front and rear of the vehicle. When the vehicle drives over a bump, these thin metal bars twist upwards to counteract the impact of the bump. They transfer the force across the chassis and redirect the load to prevent body roll. These are attached using bushings, which are prone to wear so it’s important to examine these regularly to prevent damage to the vehicle’s suspension. The anti-roll bar is connected to link rods and work in collaboration. If a link rod is broken it’s classed as an automatic MOT failure.
Whilst all of the above applies to a mechanical suspension, there is also a hydraulic suspension system which is sometimes known as hydragas. As the name suggests, this hydraulic system uses suspension spheres filled with nitrogen gas and hydraulic fluid separated by a valve. It works by the nitrogen gas compressing the hydraulic fluid capsule and providing the necessary bounce, providing the same level of suspension as a more conventional suspension system. If there is an issue with your hydraulic suspension system, you may notice vibration in your steering wheel or excessive bounce when driving. Another sign of the sphere needing to be replaced is a heavy suspension. This could be caused by a loss of nitrogen gas, which happens over time with suspension spheres.
Other signs of a suspension issue could include a cracking sound when the wheel is turned. This could indicate that you have an incorrect wheel angle caused by damaged ball joints. You may also notice that the vehicle does not bounce back well when the rear of the vehicle is pushed down.