Table of Contents
- What is Suspension?
- A History of Suspension
- What is Independent Suspension?
- What Does the Suspension Actually Do?
- How Does the Suspension Work?
- The Suspension System as a Whole
- Coil Springs
- Shock Absorber
- Is Soft or Firm Suspension Best?
- What Does the Future of Suspension Look Like?
- What Are Some Signs My Suspension is Failing?
- How Can Things Go Wrong?
- What Should I Do if My Suspension is Failing?
When you’re driving along in your car on a nice, sunny day, do you ever wonder what’s holding the car so smoothly? What’s absorbing all the little knocks and bumps in the road and keeping the interior of the cabin so tranquil?
Alternatively, you may have clicked on this article because you’re in the opposite situation: what’s going wrong with my car’s suspension? Why can I suddenly feel every bump in the road, and why does driving down this seemingly smooth stretch of asphalt suddenly feel like driving over a discarded pile LEGO?
In this article, we will run through the basics of what components make up the suspension system of your car. We’ll also include some common problems and things that tend to go wrong, as well as some signs that might suggest your suspension is on the way out.
What is Suspension?
When we mention the suspension, we are talking about the system that rests the car on its wheels. Hence, the “suspend” in “suspension.” Car bodies are “suspended” above the wheels to reduce bumps and other spine-crunching impurities on the road.
This makes sense when you compare it to the alternative. If there was no suspension – the wheel bearings and axles simply attached directly onto the body – and the car went over a bump, you can imagine how the whole thing would violently clatter around. This would be (and, in the past, certainly was) both uncomfortable and potentially dangerous for certain people in certain situations.
In cars, the main parts of the suspension are known by most as the “shocks and springs.” This system of absorbing “shocks” from the road has come to us through a long road of invention and constant reassessment of the system. We do not doubt that after 50 years and onwards, the design will continue to evolve, and we will look back and look at what we have on our cars now and think of it as ancient technology.
As far as our understanding and manufacturing capability go, the shocks and springs system is about as good as we can get right now.
Although you might not think about it, the wheels, tires, and linkages are also part of the suspension system, as well as the strut that the shock and spring are attached to. You could also include the torsion bar and anti-roll bar as part of the suspension system. All of these things help to absorb forces from the road, especially the tires – although they have less of an impact than the springs and shock absorbers.
A History of Suspension
Long before the car was invented, carts drawn by oxen used to have a suspension system involving iron chains. This allowed the platform you sat on or put stuff on to swing independently from the wheeled, wooden chassis that the wheels were attached to. By the 1600s, these metal chains were replaced with leather straps. We assume that the reason for this was to save weight, making the animals less likely to be injured and able to pull more things. These leather straps were called thoroughbraces. No car has ever been built using either one of these archaic suspension systems.
In the 1700s, the use of springs began to emerge on vehicle suspension. Although, of course, the car had not yet been invented at this point. In the 1750s, we have records of leaf springs being introduced. To avoid being taxed, many poorer people used wooden springs on a one-horse carriage instead of metal ones, which were reserved for the richer people. Although these were early designs, these leaf springs are still used on vehicles today, but usually only for vehicles transporting heavy goods, such as old trucks, vans, and the old Land Rover Defender.
We first saw the emergence of shock absorbers and coil springs in the early 1900s – these are the “shocks and springs” that are still used on cars today. The shock absorber was first used in 1901, and the coil spring was first seen on a production car is 1906.
1922 was the year where we first saw independent suspension. This was introduced on the Lancia Lambda. Nowadays, almost every car still has independent suspension. Since then, there have been constant small inventions and tweaks. For example, the inerter was invented in 2002 to be used in Formula 1 and is now used in other motorsports too. However, the system has been broadly the same for the last 100 years.
What is Independent Suspension?
You may have read the phrase “independent suspension” in the previous section and wondered, ‘What does that mean?’
If that’s you, we’ve got you covered. Independent suspension means that a wheel can move up and down without affecting the wheel on the other side of the axle. Before this time, suspension methods such as “beam suspension” were used. This meant that whatever happened to one wheel, this force was also exerted on the other side of the axle.
For example, imagine you were driving along a road, and you hit a small pothole with your front left wheel (your “offside front” wheel, if we’re being technical), but the front right (“nearside front”) wheel was simply carrying on traveling on smooth asphalt – that is, the pothole wasn’t wide enough for both wheels to hit it.
In a car with independent suspension, you probably wouldn’t even think about this. Your front left wheel would drop down into the pothole and then rise back out as you carried on driving. You’d feel a bump, and you might wince at the thought of what that little bump might do to your car. You might curse your local council. You might even stop at the side of the road to check for any damage. But it’s very unlikely that you would lose control of your vehicle.
If the car you’re driving didn’t have independent suspension, when that wheel dropped into that pothole, it would exert the same force on the front right wheel. Although it doesn’t sound like much when it’s written down on paper, it can be very dangerous. This force can cause the car to “shimmy” – that is, jump to the left or the right in the road. It will also probably cause a dramatic loss of traction to the front wheels. On top of all that, it’s incredibly uncomfortable when compared to an independent suspension system.
If you want a quick-fire definition for the next time a friend asks you if you know what independent suspension is, say, “it’s a system where the wheels across a vehicle’s axle can move up and down without affecting the other one.” And there you have it.
What Does the Suspension Actually Do?
We’ve talked about how the suspension “suspends” the main body of the car above the wheels, but there’s much more to it than that. The suspension isn’t just about making sure the car doesn’t touch the tires. It’s all about increasing traction, comfort, stability, body-roll control, and much more.
It’s not too long ago when people used to have to sit on cushions – or just grit their teeth and bear it – when they traveled any sort of distance in a vehicle of some kind. These issues were down to inefficient suspension systems. Who knows, in a few decades, we might look back at the system we use right now and think, ‘Wow, that was so uncomfortable!’
One of the main purposes of the suspension, as we have touched on, is comfort. As the car goes over bumps, potholes, and judder surfaces, these forces (or “shocks”) have to be dampened as much as possible. The primary reason for this is to protect the driver and passengers, as well as to make the ride as comfortable as possible for them. The more comfortable the car is, the better its reputation will become. The better its reputation becomes, the more people will buy it.
These shocks are absorbed by all parts of the suspension system, but primarily by the shock absorbers. Let’s be honest; you might have guessed. We’ll go into more detail about how these parts, and all the others, work in just a moment.
The tires also play an important role in dampening the effects of shocks from the road. Your tires are made of a rubber compound and filled with air for maximum amounts of traction, but this also helps begin to absorb bumps from the road. As the tire rotates over, let’s say, a rock, it molds around it slightly before continuing on its merry way.
This flexibility helps to reduce the amount of force that gets transferred up into the cabin.
Imagine it as being a little like the difference between punching a wall with bare knuckles or using a boxing glove. But please don’t actually try it! You can imagine the difference: one hurts more!
The other main purpose of the suspension is to make sure that there is as much traction as possible. If you aren’t sure what traction means, you can think of it as “grip.” Think back to the “What is Independent Suspension?” section of this article, where we saw how certain types of suspension are used to make sure a car keeps traction at all times.
It seems obvious to say, but they do this by exerting downward forces on the wheel to keep it firmly on the road. The more contact a tire has with the road, the more grip it will have. And it doesn’t take a rocket scientist to realize that, if the tire isn’t touching the road surface at all, there will be no grip whatsoever.
For example, if you turn a corner with too much speed, the weight of the car will be thrown towards the outside of the corner. The transfer of weight puts excess pressure on the outer wheel and dramatically reduces the forces pressing down on the inside wheel. In some circumstances, this can reach the point where the inside wheel (usually the rear one) can completely lift off the ground.
The wheels are pushed down to the ground through the use of coil springs and dampers on almost every production car. This results in the tire making contact with the ground again much more quickly than in a more rigid suspension system. Once the wheel is back on the road’s surface, it can regain traction, helping you to keep control of your vehicle as you’re driving along.
The two points that we’ve been through are the main reasons for the suspension in your car: comfort and traction. Without those, driving would be both unbearable and downright treacherous.
How Does the Suspension Work?
For this section of the article, we’ll briefly examine the whole suspension system and then focus on the main parts: the shock absorbers and the coil springs.
Goods vehicles and the occasional off-road cars will use leaf springs rather than coil springs. While we won’t go into these in too much detail. The long and short of them are that they can support a good deal more weight, but are considerably heavier themselves. They also make the ride feel incredibly harsh, especially in smaller vehicles and in comparison to independent MacPherson strut (spring and shock) suspension.
Leaf springs were probably invented way back in time by those clever Ancient Egyptians. They usually have multiple layers and, in the modern era, are made up of strips of metal layered on top of each other to form a spring. They are much bigger than coil springs and, as mentioned, much heavier. They make the ride far less comfortable, but can maintain much higher weights.
The Suspension System as a Whole
Let’s imagine the suspension system and work through it by following the force exerted on the car from the moment you go over a small rock in the road. Doing this will give you a good idea of what each individual part of the suspension is doing. We’ll also assume we’re talking about the front suspension, and that is has been built using a MacPherson strut.
So, you’re just driving along, minding your own business, when you drive over a small rock. In all likelihood, you won’t even notice it from your driving seat and will carry on driving as if nothing has happened. But what actually did go on down there in your suspension system?
The tire has rolled over the rock. Although, as we mentioned earlier, as tires are filled with air, this allows them to slightly mold to things they run over, reducing the shock factor. The tire will still begin to rise off the ground as it hits the rock, either running up or bouncing off it. Since the tire is wrapped around the wheel, it rises too.
Your wheel is mounted on the wheel bearing, which holds the wheel onto the steering knuckle. The MacPherson strut sits in the steering knuckle. This is just a device designed to hold the shock absorber (straight through the middle) and the coil spring (sort of wrapped around the shock absorber) effectively at the same time. The top mount of the strut attaches to the car’s body. This mounting point is usually just under the windscreen in the bottom corners.
As the wheel and tire rise off the road, you risk losing traction (if it was a bigger piece of debris or damage to the road, certainly). In this situation, the coil spring and damper then begin to push the wheel back down against the road.
At the same time, the jolt is felt as the wheel moves upwards and begins to travel up the MacPherson strut, passing through the shock absorber (and, to some extent, the spring as well). A shock absorber is filled with a liquid, some kind of oil. It is specifically designed to dampen the forces passing through it, in ways which we’ll go through in a bit more detail in a minute.
Because of the shock absorber – or “damper” – the top of the strut’s force is much reduced from the force first exerted on the wheel. It passes through the top mount and causes the main part of the bump that you may or may not hear and feel.
The spring’s second job then comes into play. The stiffer the spring is, the less the car will bounce after you’ve passed the bump. The spring works in conjunction with the shock absorber to reduce this as much as possible.
There isn’t too much to say about coil springs, to be honest. A coil spring is probably the traditional type that springs to mind (haha, sorry) when we say the word “spring.” Compared to the one you may be thinking of, though, it’ll likely be bigger and stiffer, because it has to hold so much weight.
The coil spring on each corner of the car has two main jobs, as you’ve seen from the previous section, as does the damper. It helps the shock absorber to dampen the shocks and reduces the amount of “bouncing” that goes on after the shock has passed, helping the car to return to a normal composure as soon as possible. It also helps to force the wheels back down onto the road, helping to maintain traction.
The coil spring sits in the MacPherson strut at its base and rests in the top mount. They are nigh on impossible to change by yourself unless you have a trusted spring compressor.
To change a coil spring, for example, if your old one has rusted and snapped (as happens fairly often), you’ll need to remove the strut from the car, with the spring in it. You will then need to use a special tool to get the spring out: a spring compressor. These are devices capable of holding the huge tension forces that are held in a compressed spring.
You must always be incredibly cautious when using these tools – they are known in the automotive industry as being one of the most unreliable tools in any person’s garage. Many a mechanic has been hit in the face by a spring coming loose from the compressor. That’s the best-case scenario – equalling broken bones, by the way.
We would always recommend getting a professional to work on your suspension. As much as there’s the danger of being seriously injured by the spring, struts can be notoriously difficult to disassemble without breaking something. Often, if you aren’t extremely careful, either the shock absorber will break (by twisting itself apart) or the top mount will, in the same way. In this case, you’ll probably end up having to take it to a professional to get the work done and fixed anyway.
The shock absorber is a slightly more complex piece of kit than the coil spring.
Again, it sits in the MacPherson strut, the coil spring sitting around it.
Shock absorbers, or dampers, contrary to popular belief, can’t support your car’s weight all by themselves. They are designed to reduce the forces traveling up from the road towards the car’s body to make the ride more comfortable and safer for the driver and passengers.
In terms of physics, a shock absorber is designed to convert the kinetic (movement) energy, as the car moves up and down over bumps, and to convert it into heat energy.
It does this through the use of a piston and hydraulic fluid, usually an oil of some kind.
A shock absorber is just a piston inside a cylinder. Imagine it to be a little like a blocked-off syringe with a few tiny holes in the plunger. When you push the plunger down on the syringe, with the end blocked off, you can see how its speed (or, more specifically, its acceleration) is limited by the size of the holes in the plunger. As the liquid has nowhere else to go, it forces its way through these tiny holes.
Although the plunger will continue moving down the syringe, it’s dramatically slowed down compared to when there is no resistance. You can also imagine how the harder you press, the more resistance there will be. This is basically how a shock absorber works.
The hydraulic fluid in a shock absorber gets forced through tiny orifices in the piston. These are the equivalent of the tiny holes in the plunger in our blocked-off syringe example.
Some cars, such as the Audi TT released in 2006, have shocks that are filled with a magneto-rheological fluid. This fluid adapts according to the voltage put through it, making the oil effectively stiffer or softer. It can be adjusted thousands and thousands of times per minute, depending on the road surface and driving style.
In lots of very new cars, you can get electronically adjustable shock absorbers. The size of the orifices in the piston (“the holes in the plunger” in our example) can be adjusted. They are controlled using electromagnetic solenoids. These systems allow the shock absorbers to become firmer or softer at varying times throughout your trip.
Often, the driver can select which mode they want the shock absorbers to be in. In lots of new cars, however, there are sensors all over the car to measure the wheel movement and body movement. The ECU will take the readings from these sensors and adjust the firmness on the shock absorbers accordingly.
Is Soft or Firm Suspension Best?
There’s no real solid answer to this. There are advantages and disadvantages to both types of suspension setup. You’ll find that, for most people, a softer setup is generally preferred when you’re driving on the road, but it isn’t necessarily for everyone.
In a softer setup:
- You’ll have a smoother ride. As the name suggests, the suspension makes your ride feel “softer.” It adapts to bumps more smoothly and gives the driver much more comfort compared to a firm setup.
- Your car will be better prepared for bumpy roads, no matter how extreme. Many off-road vehicles that are used in rocky terrain use a very soft suspension setup because it has so much more give in it, making the ride more comfortable for the driver and less damaging to the car.
In a firmer suspension setup:
- Although it sacrifices comfort, you’ll have better control over your car’s handling, especially in the corners. When you accelerate (which means either changing direction or speed), you cause an imbalanced force. You can see this in particular when braking heavily – note how the front of the car dips and the rear of the car rises up. The opposite happens if you set off quickly from the lights, with your front end rising up and the rear planting itself down. These two events are called dive and squat, respectively. When you go around corners, the weight is thrown towards the outside of the corner. You will feel yourself, especially as a passenger, being pulled towards the outside of the corner. This is due to the forces acting on the car. This is called body roll, and it leads to a reduced amount of traction. The weight isn’t evenly spread out over all four wheels. Instead, it’s mainly concentrating on the front wheel on the outside of the corner. Firm suspension counteracts this. The stiffer the suspension is, the more the car will hold its shape as it goes around corners, giving you more control and allowing you to go faster without losing control. For this reason, almost all track racecars will use as firm a suspension setup as possible.
You can see that having soft or firm suspension is less of a question about which is best and more to do with the type of driving you’re doing. For most people, a softer setup is generally the best way to go.
Manufacturers produce most of their consumer cars with soft suspension, and many newer cars will be built with completely adjustable suspension, as we saw in the “Shock Absorber” section.
It’s possible to change your suspension to be softer or firmer by purchasing aftermarket parts. However, you should note that your car has been specifically built with the manufacturer-installed parts in mind. So changing them may make your ride feel a little weird and, especially on newer cars with all their gadgets and gizmos, is seldom recommended.
What Does the Future of Suspension Look Like?
Nobody knows the future, but we have had some glimpses into what research and development companies are experimenting with, which are exciting to consider.
Although the technology is far from existent yet, the following concepts have been looked at:
- Electromechanical suspension systems – This system would be easier to maintain and doesn’t require fluid to be kept in the shock absorbers. Prototypes for this have already been built, and research and development are ongoing. You can see real-life examples of this kind of product in the eROT prototype developed by Audi.
- “Magic Carpet” suspension – This is a form of suspension that manually lifts the wheels before you hit a bump, through the use of linear electric motors. Although Bose originally invented the technology, they sold it to ClearMotion. ClearMotion is a company based in Boston working on a system that does just this, describing it as playing offense rather than defense. This would help to make your ride as smooth as possible. The linear motors involved in this model completely replace the shock absorbers usually found on a car.
- Other active suspension setups – Active suspension is any suspension that adjusts to the environment around it. This field is really only just emerging, so we might expect to see some world-class developments appear in the next decade or two.
- Magnetic suspension – This would involve little-to-no physical contact between the wheels and body, essentially potentially completely reducing the forces of shocks from the road to nothing. This would be far, far in the future, and who knows if it’ll ever be made to work, but it’s fascinating to consider.
Who knows what someone will come up with during the next few years? There is certainly the potential there for exponential growth in terms of the technology available to be used on suspension.
Until such a time comes, though, the standard shock and spring system that’s been used for so many years still has its place. As we currently stand, there isn’t really anything that could replace it. So, while we look to the future and imagine what the cars of 2050 might end up looking like, we are grounded in where we are today, and we know that the technology we have already can do the job pretty well as it is.
What Are Some Signs My Suspension is Failing?
If your suspension is on the way out, you may notice one or more of the following symptoms:
- An uncomfortable ride – Okay, let’s start with the obvious. If you can feel nonstop vibrating and juddering on every little bump in the road, there’s probably an issue with your suspension. There’s no real way to tell what’s wrong without taking the suspension apart, and for that, we would recommend taking the car to your local auto shop.
- If there is an excessive amount of noise coming from your suspension – this could be a sign of a problem. It usually represents something being wrong with either the top mount (if the noise comes in waves while cornering) or the shock absorber (if it’s just all the time, over every little bump).
- Excessive “rocking” or “bouncing” – when you hit a bump or slow down is likely to show you that one or more of your coil springs or shock absorbers has broken, or otherwise been damaged.
- Bump steer – Bump steer can be extremely dangerous, so if this happens to you, proceed with caution. Bump steer is when you go over a bump, and the wheels steer themselves, without any input from the steering wheel. This could be a sign of a faulty suspension component.
- Oversteer happens when you wouldn’t normally expect it to – Now, let’s be clear, oversteer can happen for any number of reasons, and the most common is that you’ve sent too much power to the rear wheels on the corner. Or pulled the handbrake, that’ll do it too. If the car seems to be kicking its butt out much more frequently than it used to, it’s a sign of a lack of traction at the rear of the car, and therefore could represent a broken spring or shock absorber.
- Understeer – Like oversteer, this can also happen if you send too much power to the front wheels, turn too hard, or are driving on a slippy surface such as snow or ice. Again, like oversteer, understeer represents a loss of traction at the front wheels, which may be caused by broken suspension components.
- Tracking problems – Although it could be that your wheels need to be realigned, you may find that, when the mechanic puts your car up on the ramp, the tracking appears perfect. If this is the case, the problem most likely rests in the suspension system or somewhere else in the steering system.
- Uneven tire wear or damaged tires – This is another symptom of the tracking problems mentioned above. If your tracking is technically all lined up, the root of the problem may lie with the suspension system (among other possible issues).
How Can Things Go Wrong?
Coil springs can easily snap, either from sudden heavy loads (such as potholes) or from rust. There’s no real way to stop them rusting – just keep an eye on them from time to time to make sure nothing has broken. Sometimes the springs break right at the top or bottom, and you may not notice them. The best way to see the spring is always to take the wheel off.
Shock absorbers can also break under sudden, intense impacts. They can also develop leaks, which prevent them from working. When changing shocks or top mounts, you may accidentally twist the shock absorber in its casing, which also breaks it.
Other parts of the suspension can also fail. When you’re looking at getting this problem fixed, we would always recommend getting a replacement part for whatever has broken, rather than trying to fix it in some way. Replacement parts are much stronger than hastily-welded ones.
What Should I Do if My Suspension is Failing?
In short, get it fixed.
As with all problems, the longer you leave it, the worse it’ll get. Getting it fixed as soon as possible is both the safest and the most cost-effective way to be.
Even for people who know their way around cars, changing out suspension can be a tricky business and can easily go wrong. We would recommend taking your car into a garage to get it fixed unless you are confident of being able to do the job yourself.
When you take your car into a garage, how much you pay will depend on a few different factors, including where you live, the garage’s reputation, the type of car you drive, and the quality of the part that you get ordered. Different garages will also charge different mark-up rates on the part and labor rates for the work, so bear that in mind.
When you’re talking to the mechanic, tell them all the things you have noticed that make you suspect something is wrong with your car’s suspension. They will use an automotive ramp or inspection pit to look underneath your car and give everything a good tug to see if anything is loose. They’ll also remove the wheels and inspect everything there.
For one new coil spring on a front wheel, expect to pay about $150 – $200, including labor, and approximately the same, maybe slightly more for a new shock absorber. Ensure that the labor cost isn’t doubled though, if you’re having both jobs done on the same strut – the shock absorber can be changed at the same time as the strut, so shouldn’t take too much extra labor.
The suspension is a vital part of your car. Without it, you would be writhing around in discomfort after every single journey you make. It’s good to be aware of what all the different parts do and how they work together to know if a problem begins to arise.
We hope you’ve found this article interesting and that you know more about your car’s suspension than you did before clicking on it.
As always, thank you for reading, and be sure to leave us a comment at the bottom of the page.