Car suspension allows vehicles to pass over bumps without you feeling a thing. It is mainly made up of your tyres, tyre pressure, springs, shock absorbers and linkages. Suspension must also protect the vehicle and passengers from damage and wear, and keep the tyres in contact with the road as much as possible. But that's not all. There's plenty more that a suspension system does, most of which goes completely unnoticed.
By the end of this article, you will understand:
- What suspension does
- What car parts make up a suspension system and their roles
- Why front and rear suspension differ
- How to spot suspension problems and what to do about them
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Leaf Springs - A simple form of spring that first appeared in the mid-17th Century. It takes the form of a slender arc-shaped length of spring steel and can be attached directly to the frame at one or both ends.
Dampening - The process of controlling or stopping a spring coiling and uncoiling. Otherwise, the spring would not be able to disperse the energy it absorbs.
Hydraulic Fluid - The liquid which transfers power in hydraulic machinery. This is the liquid that controls the dampening process.
Sway - The term used for a car body rolling, or the weight shifting, to one side when you go around a corner.
MacPherson Suspension System - Developed by Earle S MacPherson of General Motors in 1947, this is the most widely used front suspension system, especially in Europe. It combines a shock absorber and coil spring into a single unit, providing a more compact and lighter system.
What Does Suspension Do?
If a road were perfectly flat, there would be no need for a suspension system. However, even a freshly paved motorway has subtle bumps that apply forces to your car's wheels. Any bump in the road causes the wheel to move up and away from the road surface. Without something to intervene, all the force would transfer to the frame and move your car in the same direction. This could mean your tyres lose contact with the road and you end up doing a wheelie. Then, gravity would kick back in and slam your tyres back onto the road.
As these are some of Newton's Laws of Motion, they will affect your car. Nothing can stop that. That's why every car needs a system to absorb the energy of the wheel and allow the rest of the car to ride undisturbed.
That's the suspension system.
Suspension is part of the chassis. It supports your car's handling and ride quality, even though the two are at odds with each other, as well as the other jobs mentioned above.
In short, suspension keeps you in control of your car.
How Many Car Suspension Parts Are There?
There are 7 main suspension parts. These are:
- Shock Absorbers
- Anti-Roll Bars
- Anti-Roll Bar Link Rods
- Bottom Suspension Arm
- Top Strut Mount
Each part performs a different role, as laid out below.
The most common spring found on modern cars and light vans is the coil spring, but you can also find leaf springs. They coil and uncoil to absorb the motion of the wheels. Due to where springs are fitted, engineers often talk about the sprung and unsprung mass of a car.
Simply put, sprung mass is the vehicle's mass supported on the springs, while unsprung mass is the mass supported between the road and the springs. The stiffness of the springs affects how the sprung mass responds while driving. Generally, luxury cars are loosely sprung (and so are super smooth to drive) while sports cars are tightly sprung. This can make them more uncomfortable to drive but allows you to be more aggressive through the corners.
However, springs alone can't provide the smoothest ride. They absorb energy well but don't get rid of it. This means that they would continue to bounce on their own if not for the next suspension part.
Shock Absorbers control unwanted spring motion through 'dampening'. They sit between the frame of the car and the wheels and absorb the energy from the springs. A shock absorber contains hydraulic fluid and acts like an oil pump. This fluid slows down the movement of the shock absorber which, in turn, slows down the movement of the spring.
In modern cars, the faster the suspension moves, the more resistance the shock absorber provides. This is known as being 'velocity sensitive'. This process allows the shock absorbers to control all the unwanted motions of a moving vehicle, including bounce and sway.
Most cars use a MacPherson suspension system. In this design, coil springs and shock absorbers are fitted together and known as a strut.
Struts still dampen the spring's bounciness, but also provide more structural support for the suspension than shocks do. They are fitted to the front of a car and the top is connected to the body and the bottom to a suspension arm.
Anti-roll bars give a vehicle extra stability. They are metal rods that span the entire axle and join the sides of the suspension together.
When one side moves up and down, the anti-roll bar transfers movement to the other wheel. This creates a more level ride and makes for smooth cornering.
Anti-Roll Bar Link Rods
Link rods connect the suspension parts to either end of the anti-roll bar. They are usually light metal or plastic rods with a ball joint on one or both ends and help your car when one side of the suspension moves but the other does not.
For example, you drive over a speed bump the full width of the road, the suspension is equally compressed. This allows the anti-roll bar to pivot without stress or strain. However, if one wheel hits the speed bump and the other doesn't, one end of the bar is raised and twists. This twisting force is transmitted through the link roads, which eases the strain on the anti-roll bar.
Bottom Suspension Arm
The bottom suspension arm is one of two control arms in the front suspension system. It connects the car's frame to the front wheel assembly and holds the front wheels on the road.
These arms can swing up and down as the wheels roll over bumps, allowing your car to press smoothly ahead.
Top Strut Mount
The top strut mount attaches the struts to the vehicle. It also insulates against tyre noise and vehicle vibrations.
Think of a strut mount as a sandwich. One side bolts to your car, the other side to the strut and, in the middle, there is a rubber-like insulating material. As your car goes over bumps, the impacts push and pull at the mount which cushions these impacts to reduce the jarring effect and keeps the cabin quiet.
Here's how all these parts fit together in a traditional MacPherson front suspension system, complete with steering assembly:
Why Do Front & Rear Suspension Differ?
Most modern cars are front-wheel drive. As a result, they need more flexible, responsive suspension at the front of the car to accommodate the steering system. This means they have independent suspension.
Independent suspension allows each wheel on the same axle to move on its own. So, if only one wheel passes through a pothole, it can adapt to the dip in the road without affecting the wheel on the other side.
However, rear suspension doesn't need to accommodate a steering system. This means they are usually 'dependent suspension systems'. These have a rigid axle connecting the wheels. This axle is kept in place by leaf springs and shock absorbers. If independent suspension is also used at the rear, the vehicle will have four-wheel drive.
While cars can use the same suspension system at the front and rear, most vehicles use a mix of dependent and independent. This is because independent suspension is more expensive to produce and not always necessary at the rear.
Car Suspension Problems
There are a range of symptoms that can indicate a problem with your car's suspension. These include:
A rough ride. This usually means that your car's shock absorbers are worn. When they weaken, any bump can send your car flying without anything to pull it back to the ground. This decreases your car's performance and makes it harder to control.
Drifting or pulling to one side. While this can also indicate a problem with your tyres or wheel alignment, it could be due to a broken track rod, spring or suspension arm. You should check all possible causes or get a qualified mechanic to do it for you.
Car sits low or the nose dives. If you notice the front of your car dipping or a clunking sound every time you go over a bump or turn a corner, you might have a broken spring. If you ignore this, you will put more pressure on the shock absorber which then can also fail as neither will be able to support the car.
Damaged or oily shocks. A worn shock or strut is incredibly dangerous. They can allow excessive weight transfer from side to side and front to back. This affects your handling and your brakes and also means that your tyres have less grip on the road. If your shocks look oily or greasy, they are leaking fluid and require immediate repair.
Excessive bouncing when you press the bonnet down. If you lean on your bonnet while parked and it bounces more than 2-3 times after you release the pressure, your suspension is failing.
What Do I Do If I Notice These Problems?
You should never ignore a problem with your car's suspension. It plays a crucial role in keeping you safe and comfortable on the road. If your car does have a problem, book an appointment at a local garage to get it sorted as soon as possible. Even if your suspension system is fine, they will be able to find the actual cause and get you back on the road again safely.
Car suspension keeps you in control of your vehicle and allows your wheels to move and react to the road. It does this without affecting your handling or ride quality. Key suspension parts include the springs and shock absorbers. These usually take the form of struts in a MacPherson system (the most common in modern cars). Front and rear suspension can be the same but are usually different - simply because an independent system is more expensive to produce.
If you notice any problems with your car's suspension, such as poor ride quality, drifting or pulling to one side or damaged shocks, you should book an appointment at a garage near you as soon as possible. Car suspension plays a huge role in keeping you safe, so you can't allow that to become compromised.