One of the trickiest parts of tuning, car suspension is a vital element of any project build. Luckily, we’re here to tell you all about it…
Words by Stav.
What is car suspension and why do we need it?
Car suspension makes up a huge amount of the parts underneath the body. In fact, every single part that somehow connects your wheels to your car counts as suspension; and that’s a hell of a lot of parts. Without suspension, aside from having nothing to bolt your car’s wheels to, there would be no way for your wheels to move independently of the chassis, but why we need that to happen is a little more complex.
First up, you could remove a car’s shocks and springs and replace them with a solid bar, meaning no movement at all, but the car would not only become about the most uncomfortable thing ever to drive normally, but it would actually handle like absolute crap even on the flattest surface. While low and stiff is considered good for handling, even the stiffest suspension moves far more than you might think, and trust us, some people have tried running solid suspension on cars, even in F1; and it really never works.
You might think, “well go-karts have no suspension, and they handle awesomely”, but even that’s not actually true. Go-kart chassis are designed to have a lot of flex in them, so the chassis itself works as the suspension; a rock-solid go-kart would handle just as badly as a car with solid bars instead of shocks and springs. Even the lightest cars weigh hugely more than the heaviest go-karts, so even if you designed a car to use the chassis as suspension like a Kart, for a car chassis to have enough flex in it to work as suspension, it would be so floppy that the car would be totally undrivable. Basically, for a car to handle, you NEED correctly working suspension.
From a comfort point of view, the need for suspension is much more obvious, but thinking the softer the better isn’t true here either. If it’s too soft, it’d be so wallowy that the car would bob and rock over even the smallest bump or tiniest throttle, brake, or steering movement, so you’d probably feel sick by the time you got to the end of your street! So, as you can see, suspension set-ups are all about finding the goldilocks zone: nothing too firm, but nothing too soft either.
Be sure to check out our guide to the best car suspension brands in 2023.
Car suspension components
It’s a subject that covers far more than just the shocks and springs most of us imagine. In fact, those are just a fraction of the parts involved. For Suspension Part 1 though, we’re dealing with static suspension and that’s purely because the vast majority of cars come with that as standard. We’ll get on to more specialist active suspension, like hydraulics and airbags later, but for now it’s worth knowing that however you choose to modify your suspension, this will be the stuff you’ll be tweaking or taking out. Here’s what’s what…
Car suspension coil springs
These are the main suspension components that stop your car’s chassis from just sitting on top of the wheels. Aside from doing that, they have two other main jobs; to cushion the car over bumps or potholes, and to help the wheels keep in contact with the ground when one or more wheels hits a rough spot. How they do both jobs is simply by doing what a spring does best – compressing or expanding, allowing the wheel that hits the bump or dip to move up and down in the wheel arch, while (ideally) leaving the body and the rest of the wheels moving along as smoothly as possible.
The two main variables with springs (aside from being the correct diameter to fit your car,) is length, and stiffness – often known as spring rate. You don’t need us to tell you that a shorter spring will lower your car, but go too low (unless you got shortened shocks too), and you’ll end up bottoming out the shocks, which is really bad for handling.
Spring rate is the main (but not only) factor in how hard your suspension is. Springs for specific applications tend to be already rated at a suitable stiffness for that car, but they’re not always to everyone’s tastes, and depending on what you’re using the car for, stiffer or softer ones may be needed.
These are also known as dampers, and this name gives a big hint to what they’re there for. The job of a shock absorber is to control the movement of the spring. Without a shock, the spring would just keep moving, making for a bouncy and uncontrollable ride which is no good for performance or comfort.
Shock absorbers come in two main forms, either with the coil spring mounted on top (or totally separate to the shock), or as coilovers, where the spring literally sits around the shock. While the main reason for the invention of coilovers was to create a more compact and lightweight design, for most of us, the main plus point of coilovers is that the spring seat is threaded to the body, allowing it to be easily moved up and down which adjusts the ride height of the car.
While most standard and budget aftermarket shocks aren’t adjustable, higher-end setups are adjustable for stiffness (more on this later), and full-on race-spec items are not only multi-way adjustable but also feature trick additions, such as remote reservoirs to further improve their performance.
These tend to be found on the back of French hatchbacks, though they’re fitted to other cars too. Torsion ‘springs’ would actually be a better description of what they do, which is effectively replace the job of coil springs. They work in a similar way to a go-kart chassis – the vertical movement of the wheels acts against the torsion bar, which although it’s made of solid metal, is able to twist slightly, allowing the wheels to move up and down when needed.
Just like the springs they replace, thicker and stiffer torsion bars are available for many popular performance cars, and while they’re not as straight forward to replace as springs, they can be uprated in just the same way.
These are the hinged arms that not only mount your wheel hubs to your subframe/chassis, but also control the arcs of movement as the wheel moves in the arch, which are key to your car’s handling abilities. As already mentioned, wheels move up and down in the arch as allowed by the spring and shock absorber combo, but on most suspension designs they don’t just move up and down. They can in fact move in all directions depending on the type of movement the car is doing at the time.
Standard control arms are designed with the intention to put the wheels at an optimum angle for the handling characteristics the factory required, but when ride heights or the use of the car is changed from standard, the control arm settings may become far from optimal. This is why adjustable control arms, which allow front and rear camber, toe, castor, and even wheel track width adjustment, are so popular on tuned road and track cars.
Anti-roll bars are another form of torsion bar, but these are fitted to the front and rear of almost all cars these days. Their job is to supplement the conventional suspension springs rather than replace them. As you might have guessed, ARBs exist to help resist body roll – if you simply made the shocks and springs stiff enough to eliminate body roll on their own the suspension would be too hard to work properly on the vast majority of surfaces.
Thicker and stiffer ARBs are a common aftermarket upgrade, and some high-end versions are actually adjustable; in fact, some race cars have in-car adjustable ARBs, enabling the driver to adjust roll stiffness while out on track! ARB settings are a good way to change the handling characteristics of the car too, with a stiffer rear bar tending to increase oversteer, and a stiffer front bar tending to increase understeer.
Rose joints and car suspension
These, in car suspension use, tend to be used to replace suspension bushes on the ends of suspension arms in fast-road builds and especially for race use. These are solid metal spherical bearings that will allow the arms to move in their specified arcs just as intended from the factory, but while totally eliminating the flex the rubber bush gives. The main advantage of getting rid of the flex is improved precision of suspension and steering feel, but the side effect is a stiffer ride and a much shorter life span than production rubber joints.
These are the items that locate the top of the suspension strut in the correct position on the car’s chassis. From the factory they tend to basically be a large rubber bush that absorbs the stress and vibration that would otherwise be transmitted to the chassis from the suspension.
Uprated items tend to be made of either polyurethane or solid metal, with a rose joint to mount to the shock absorber (helping to improve handling response and control). Some aftermarket top mounts allow the shock and spring position to be relocated a few centimeters within the suspension towers, giving you a decent amount of camber and sometimes even castor adjustment.
On standard production cars these are the rubber mounting points on the vast majority of standard suspension components, and they allow two metal parts to be connected without actual metal on metal contact. This drastically reduces the vibration and noise that would exist if the components were connected with a solid metal joint, and decreases wear too.
On tuned cars these soft rubber bushes are commonly replaced by stiffer polyurethane items, reducing movement and improving suspension response. On full-on race cars many bushes are replaced by solid metal mounts to totally eliminate flex, but this is at the expense of noise, comfort, and long-term wear; all things that aren’t much fun on a road car, but not an issue on a racer.
Check out our guide to suspension bushes to learn more.
Not all cars have these, as some have the suspension arms mounted directly to the chassis, but subframes are the solid frames that the suspension arms are connected to on the front or rear of many cars. Subframes are specially designed so the suspension arms are connected at the perceived perfect position for the standard production vehicle, but on a modified version of the car these positions are often far from perfect.
Unfortunately, modifying a subframe is no easy task and it’s rarely done outside of hardcore race cars. But on some vehicles, custom tubular subframes (which save weight and mount the arms in an optimal position for race use) do exist; if you can afford them that is!
Static car suspension designs
Over the last century there has been a countless variety of suspension setups, though many of them have fallen out of fashion. These days there are just a few designs still in regular use, and while all of them have advantages and disadvantages, they can all be very effective on the road and track. Here’s a run-down on the most popular designs…
Multi-link car suspension
This is the most modern and complex suspension design. In theory, this makes it the best, but the complexity means it needs sophisticated 3D computer simulations to accurately design, so it’s not as common on specially made race cars as you might imagine. Multi-link setups have three or more arms per wheel, which means every possible arc of movement can be individually designed without it affecting another. For example, if the designers wish, the camber can change as the wheel moves up and down without it affecting toe or castor like it tends to with other suspension designs.
In reality, getting suspension geometry perfect is incredibly complex and manufacturers spend millions using sophisticated computer programs to try and get it right. But once the car is modified beyond its original intentions, these things are likely to be less than perfect once again. Having said that, multi-link – provided you have fully adjustable arms – gives a tuner an incredible range of geometry changes at their fingertips, and while some racers may consider it overly complex, it does allow an almost infinite range for you to tweak the geometry to your heart’s content.
This is the most common front suspension setup, mostly because it’s simple and cheap. While it’s not outstanding in any way, it’s effective enough that it’s used on countless high-performance production and tuned cars. This setup consists of a single lower arm, which the wheel hub bolts to, as well as a smaller arm usually facing forward at an angle to prevent the single lower arm moving backwards and forwards in the arch.
The main disadvantage of this setup is lack of adjustability and the fact that any upward or downward movement of the wheel quite dramatically affects camber angle and even position in the arch. This means the handling, theoretically, isn’t as good as a double wishbone or multi-link setup, but the reality is, with the right settings, a MacPherson setup is perfectly effective, even on some of the world’s fastest track cars.
This setup is generally considered to be the best for overall performance. It’s fitted to a wide variety of sports and supercars, and is certainly the most popular design for purpose-built race cars. Having said that, it’s fitted to an amazing amount of normal cars too; with some big Honda and Peugeot saloons having double wishbone suspension on the front from the factory.
Double wishbone suspension basically consists of two, parallel, V-shaped arms mounted top and bottom, directly joined to the wheel hub, and the suspension shock and spring is mounted through the Vs. The main advantage of double wishbone is that the movement of the arms gives a more linear and predictable change to the geometry as the wheels move up and down in the arch. This means a good double wishbone setup can give great cornering grip, and is especially useful on a tuned car which has adjustable arms. Ultimately, it makes it much easier to work out what the effect of your geometry changes will be compared to some other designs.
A big disadvantage of double wishbone suspension, aside from the fact it takes up quite a bit of room under the car, is while adjustment is predictable, having just two suspension arms per wheel means adjustment of one geometry parameter tends to affect at least one other. So, a lot of effort has to be put in to tweaking each adjustment point to get everything as you wish.
Not to be confused with torsion *bars* (which are mentioned above), torsion beam suspension is a relatively similar design, keeping the standard spring and shock combo that has been widely used since the 1980s. Torsion beam rear ends are as basic as suspension gets, being simply a semi-trailing arm each side of the car, solidly connected to each other by the horizontal torsion beam.
This torsion beam allows some independent movement between each wheel, but not complete freedom – in fact it acts a lot like an ARB does to help resist body roll. The main reason this setup is so popular in smaller cars is it’s very compact, giving more rear seat and boot space inside the car. However, the majority of the best handling hot hatches from the last three decades have had this style of rear suspension, so while it’s basic, it evidently does the job!
This setup is rare to see outside of trucks and 4x4s these days, but it’s the rear end setup fitted to many legendary cars such as the AE86 Corolla, Mk1 and 2 Escort, and countless American muscle cars. A live axle is a large metal bar running between the two wheels, with the rear differential mounted in the middle, and the driveshafts running through the hollow bar to each wheel. The shocks and springs are mounted on top of the axle and join it to the chassis, and there’s usually other locating bars between the axle and the chassis to try and prevent it moving around under hard use.
While common myth states live axles are the worst thing in the world, the reality is different. Although they’re as basic as you can get – they don’t allow the wheels to move independently of each other and add significant unsprung weight (more on that later) – they don’t allow body roll or ride height to affect camber or toe settings like other setups do. So, for flat surfaces and straight-line traction, a live axle can actually be a real advantage.
While they’re certainly not the most sophisticated setups, semi-trailing arms were very common on the rear of production cars in the ’80s and ’90s, and are still in widespread use today. Their basic design consists of one large suspension arm attached to each wheel hub, that is connected to the chassis via a hinged joint at the front, and faces forwards and inwards at an angle. Semi-trailing arms were popular as they give fairly neutral handling even when the body is rolling.
But when the ride height is lower than standard, they tend to add quite a lot of excessive camber and toe out, neither of which is ideal for grip – especially on rear-wheel drive cars – meaning adjustable arms tend to be needed to counteract this for maximum performance. Unfortunately, and due to the size of most semi-trailing arms, acquiring uprated adjustable arms for these setups isn’t as easy as it is for cars fitted with multi-link suspension.
You’ve probably heard people talk about unsprung weight when talking about cars, but what the hell is it? Well, basically it’s the weight of everything not supported by the suspension springs, so it’s practically every car suspension component, plus your wheel hubs, brakes, wheels, and tyres. So that’s what it is, but why is it important? Well, unsprung weight has a much bigger effect on a car’s performance than sprung weight, which is everything on the car that sits on the suspension springs.
As you know, weight is the enemy of all aspects of performance, especially handling, so a heavy unsprung mass is a bad thing, and any way you can reduce it can make a really noticeable improvement in handling. The way most people reduce unsprung mass is to fit lightweight wheels, but replacing the standard heavy suspension arms and even subframes with lightweight tubular arms can have a massive effect too. In fact, some hot production cars, like certain Impreza STi models, come factory fitted with lightweight arms in comparison to the lesser-spec models.