What Is Suspension?
Ellie Dyer-Brown, 7 months ago
5 min read
- Suspension
- How it works
FixMyCar explains what suspension is and how it works.
Whenever you hit a bump in the road, your car's suspension system functions in the background to keep the ride as smooth as possible. It's an unsung hero - each journey would be much less comfortable without it.
If you've ever found yourself wondering how suspension systems work, this guide is for you.
Contents
What is car suspension?
Suspension is a shock-absorbing system that allows the wheels to react to the road and helps you control the car. When a vehicle handles well and has good ride quality, it is primarily due to the suspension.
Glossary
Here are the terms you need to be aware of.
Dampening refers to stopping or controlling a spring from coiling and uncoiling, which allows it to disperse the energy it absorbs.
Sway describes the weight of the car body shifting, or rolling, to one side as you turn a corner.
Hydraulic fluid is used to control the dampening process by transferring power.
Leaf springs are thin arc-shaped lengths of spring steel that can be attached to the frame at one or both ends. This spring type was introduced in the mid-17th century and is mainly found in older cars and pick-up trucks.
Suspension components
There are eight main suspension components to be aware of.
Let’s take a look at some of those in more detail.
Shock absorbers
Springs are excellent at absorbing energy but not so much at releasing it - they tend to rebound uncontrollably, which results in terrible ride quality and handling in a car. Shock absorbers solve this problem by releasing the spring’s energy in a controlled way.
Sometimes, shock absorbers are called dampers because they aid the dampening process (see glossary). They look like thick, stubby bicycle pumps, and depending on the suspension system, they either sit close to the coil spring or inside it. When a shock absorber is inside the spring, it is known as a strut.
Shocks are typically divided into two sections. The top section, or outer tube, contains a piston. The lower half of a shock absorber is known as a reserve tube. It is bolted to the axle and filled with hydraulic fluid.
When the car hits a bump, the axle rises, compressing the spring and forcing the piston to move into the fluid, which is forced upwards through tiny holes. The piston starts rising as the spring rebounds, changing the fluid's direction. This process creates pressure in the shock absorber, slowing the piston and, as a result, the spring’s rebound.
Springs
Most modern systems use steel coil springs, though, as discussed, some vehicles use leaf springs. The torsion bar (also known as an anti-roll bar) is another type of spring, though it doesn’t look like one.
Anti-roll bar
An anti-roll bar is a long piece of metal attached to the suspension at the wheel end and the car at the other. When you hit a bump, it twists to absorb the energy.
Struts
Every wheel has a shock absorber or a strut, both of which are designed to provide better ride control. Struts are a major structural part of the suspension, combining a shock and spring assembly in a compact unit. They replace the upper ball joint and control arm used in conventional systems and take up less space than shock absorbers.
In cars with MacPherson suspension systems, the top strut mount attaches the top of the strut to the chassis, playing a pivotal role in insulating the strut from the vehicle and reducing noise and vibrations.
Control arms
Control arms are found on the vast majority of road-going suspension systems. They are situated at the front axle at each end of the two front wheels and can be L-, A-, or wishbone-shaped. They have connection points at each end for attaching a wheel’s steering knuckle to the frame.
At the vehicle’s frame, control arms are connected to a hinge by bushes and bolts, and at the steering knuckle end, they are connected via a ball joint to allow the wheels to move smoothly.
Many cars have an upper and lower control arm for each front wheel, connecting to the highest and lowest steering knuckle joints, allowing extra control and stability. However, MacPherson suspension systems only have a lower control arm; a strut replaces the upper arm.
Bushes
A suspension bush is a hollow, solid or oil-filled rubber component fitted between many suspension parts. It prevents erosion from metal-on-metal contact and reduces vibrations from the road.
Learn more about suspension bushes.
Car suspension system types
MacPherson suspension system
This is the most widely used front suspension system. It was developed by Earle S MacPherson of General Motors in 1947 and incorporates a coil spring and shock absorber into a single unit, allowing for a more compact system.
The top of the shock absorber is attached to a suspension turret, and the lower part is attached to the wheel hub. Control arms extend from the hub and are attached to the frame.
Independent suspension
When a suspension system is ‘independent’, each wheel (usually the front pair) is attached separately to the car body, allowing it to move independently of the other.
Non-independent systems are often found on trucks and vans and are more cost-effective. The suspension systems are connected by an axle fitted with a damper and leaf springs at each end. Consequently, forces acting on one side of the vehicle will also act on the other.
Some vehicles, such as the Volkswagen Golf S Mk 7, feature a halfway version at the rear, known as twist-beam rear suspension. It allows more independent movement than an axle but less than an independent system. Its main benefits are that it is simpler and cheaper.
Double-wishbone suspension
Double-wishbone suspension has two arms per wheel, one above the other, extending from the wheel hub to the car’s frame. They are made of either aluminium or pressed steel. The lower wishbone is fitted with a shock absorber inside a steel spring, which attaches to the car body at its other end. You can have this system on all four corners of a vehicle.
Air suspension
Air suspension is an increasingly popular feature on SUVs and luxury cars. This system uses air springs (essentially air-filled containers), rather than traditional steel coil springs. As each air spring moves, the system adds or removes air to maintain comfort.
Powerful microprocessors control the amount of air and can make the springs operate together or individually. They can also raise the car when travelling over rough ground, which is handy for off-roading, and lower it to improve ride quality and fuel consumption.
This is another example of why modern car batteries are more expensive to replace; complex electrical systems require more power.
Adaptive damping
Dampers (aka shock absorbers) are becoming more complex, like many car parts. Whereas they used to react to the movement of the car’s springs, some can now control events intelligently.
For instance, magnetic dampers contain a ferrous liquid. When an electric current passes through, it can immediately alter the liquid’s viscosity, or thickness, according to the force being applied. Other systems control the fluid’s flow using a solenoid.
Why are vehicles fitted with air suspension?
Air suspension has many advantages over traditional suspension systems. It transmits less vibrations to the road and nearby structures like bridges, which reduces wear, creating fewer potholes. For this reason, it is considered to be more environmentally friendly.
Additionally, air suspension allows drivers to adjust the car to suit their preferences by changing the ride height and handling. Overall, it provides a smoother ride.
What is car suspension alignment?
Problems with the suspension often affect the alignment of the wheels, causing the car to veer to one side and the tyres to wear unevenly. When this happens, a wheel alignment is required, which involves the mechanical adjustment of the suspension system to ensure the wheels are in the correct place.
Find out more about wheel alignment in this guide.
Think there might be an issue with your car's suspension system? Whether you need a repair or you'd like it checking for your peace of mind, FixMyCar can help you find the right garage at the right price.
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Written by Ellie
Ellie is FixMyCar's Content Writer. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers in a language they understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.