car tuning: suspension
Suspension performs an extremely important function for your car: it keeps the tires on the ground. Your tires, no matter how good they are, can’t do their job properly if they aren’t touching the road. It also, in the course of doing its job, helps to make your ride more comfortable by absorbing impacts from the road surface.
There are an almost infinite number of options for your car’s suspension. Between spring rates, spring heights, shocks, structs, coil-overs, sway bars, strut-tower bars, adjustable control arms, polyurethane bushings, and probably a ton of options I can’t even think of, suspension adjustments are basically limitless.
What kind of suspension modifications or upgrades you make to your car depend on the type of suspension your car left the factory with.
Where to begin
The first step in any suspension tuning or modification is understanding what you’re starting with, what the capabilities of your car’s suspension are as it was engineered to be. Knowing your stock suspension will help you know where you want your suspension to end up. If you have a newer car, this is easy—its how your car came. If you have an older car, though, you may need to bring the car up to what is often called “Stage 0”, or bringing the car back to stock.
Now, I know what you might be saying: “But I don’t want to spend the money to get my car back to stock, I just want to upgrade it.”
I’ve thought that before as well. And I don’t disagree with that sentiment either. Money is a finite resource and cars are expensive. In fact, on my Volvo 245, upgraded the blown out shocks and struts and the cut stock coil springs with Bilstein shocks and struts and IPD’s sport lowering springs. Fun fact: buying lowering springs actually increased my car’s ride height.
I definitely didn’t put the car back to Stage 0 before upgrading.
Did I lose anything or miss out on anything by not doing this? Yes and no.
I missed out on the opportunity to know what the car handled like before the upgrade, giving me some sense of the improvement that was made. What I didn’t miss out on was spending twice the money on parts.
Once you’ve gotten to know your cars suspension and handling (or decided to forgo that process) the next step is to decide what your goals for your suspension are.
What’s the plan?
Knowing how you want to use your car will help inform what suspension modifications you make—and how extreme you make them. There are a few steps of suspension modification that you can perform to meet different needs.
Below, two goals are covered: making your daily driver into a spirited, backroad carver and building a dedicated autocross or track car. Each has its own purpose, one for getting you to and from work, while letting you have some fun on the weekends and the other getting you the sharpest handling for laying down your best lap times.
Your Goal: A Spirited Daily Driver
In this circumstance, you have a daily driver that you want to make more fun to drive. We’ve all been there. Half of modifying a daily driver is increasing stability so that you can have more fun with it on the weekends. The other half is not compromising the comfort of the car—at least not too much—since you’re going to spend most of your time in this car commuting and sitting in traffic on the country’s less-than-ideal roads. This stage of modification needs to bridge the gap between performance and comfort.
Shocks and Struts
Shocks and struts are an easy way to improve handling without requiring much else to be changed. As the part of the car that helps to dampen the impact or “shock” of uneven road surfaces, they’re a truly important part of your suspension. By adding shocks and struts that have an increased damping and rebound rate, you can stiffen up your car’s suspension without having to replace other parts. When looking at sport or higher performance shocks and struts, you can also find adjustable models that allow you to increase the rebound (and sometimes damping rate) for sportier driving, then let you reduce that rate to make your daily commute more comfortable.
Sport springs tend to bridge that gap between comfort and performance fairly well. They live between the factory springs aimed mostly at comfort and a full coil-over conversion that’s aimed at spending your days at the track. They come in a couple of different varieties, standard height but increased spring rate, or mild lowering with an increased spring rate. Both options give you a stiffer ride, reducing body roll and increasing stability. Lowering springs also lower the car’s center of gravity and their shorter length can provide a tiny decrease in overall weight. Both provide improved handling characteristics, however the lower center of gravity does add a slight bump in handling over the stock height variety. Sport springs also tend to allow for less required modification to things like suspension geometry because of the mild nature of the lowering they provide. They work the best when paired with higher performance shocks and struts.
No matter what type of drivetrain you have, your car likely has at least one sway bar attached to it. The sway helps tie the left and right sides of your suspension together in order to keep your tires planted while cornering—fighting a car’s tendency to lift the side of the car on the inside of a turn, ultimately providing more traction.
When trying to improve the handling of your car using sway bars, you have a couple of options. If your car only came with one sway bar—usually on the front of the car—you can add a second sway bar to the rear of the car. If your car came with two, you can increase the size of either the front or rear sway bar (or both) depending on whether your car oversteers or understeers. You’ll want to keep in mind when increasing the size of the sway bar not to increase this too much. Having too much sway bar can cause a harsh ride and poor handling characteristics. As with any other modification, the sway bar should be changed in conjunction with other modifications so that they all work together.
Strut Tower Bars
While springs, shocks, struts, and sway bars all increase the rigidity of your suspension from underneath your car, strut tower bars help do this from the top. Cars, especially those with unit-body construction, flex a little bit when cornering. This flexing isn’t a problem under normal driving conditions, but when you start pushing your car harder and cornering faster, your suspension geometry gets moved slightly, which can have an adverse effect on higher-performance handling. Similar to (but not exactly the same) how a sway bar connects the left and right sides of your suspension, a strut tower bar connects the top of, well, the strut towers in your car, helping to hold them in place and pushing against each other when cornering at high speed. When this happens, your suspension geometry doesn’t change nearly as much and your suspension (and tires) are able to do their job better.
There are a ton of options for strut tower bars on the aftermarket, so you’ll have plenty of brands and styles to choose from. When adding one to your daily driver, you don’t need to worry as much about the diameter as you won’t (or at least shouldn’t) be reaching racing speeds while carving up that back road. The main consideration you should be looking for in your street-oriented strut tower bar is that it is performance oriented rather than just being an aesthetic add-on. Installing a strut tower bar is fairly straightforward, you’ll likely only need to unbolt the strut mount nuts on the top of your strut tower to in stall it.
While you can find a “triangulated” strut tower bar for most makes and models, these will likely require drilling holes into your car’s firewall to mount the bar in addition to bolting it to the strut towers themselves. For most street applications, this style of bar is overkill.
Polyurethane bushings are a modification that you’ll read about all over the online forums. These replace your rubber bushings with polyurethane ones that are more rigid, allowing less flex in your suspension. If you’re in need of a bushing replacement and are looking to improve your handling, they make a great add-on to your car.
There are a couple downsides to polyurethane, though. They often squeak as instead of flexing when your suspension moves, they rub against the metal parts. When installing polyurethane bushings, you need to make sure you use the suggested grease. You may also find that you occasionally need to take your suspension components apart and re-grease them.
The other downside is a harsher ride. This is for the same reason as the squeaking—they don’t flex nearly as much as the factory rubber bushings. As with any suspension modification, it’s up to you whether this effect is worth the performance gains.
Your Goal: An Autocross or Track Car
You have a dedicated car that you autocross on the weekends and take to the track to test your driving skills. Modifying a car specifically for racing and track use gives you a lot of room for deciding what modifications to make and how much you’re willing to spend on them, especially since you don’t need to take comfort during your daily commute into account.
Shocks and Struts
For your dedicated track car, you have a wider variety of options available to you. In this circumstance, you won’t be hindered by options specific to your make or model, since you’re most likely going to be doing a lot of fabrication and modification to your suspension to give you the most adjustments possible.
This extends to your shock and struts. There are a lot of high-performance shocks and struts available, so it really comes down to how you’ll be using them in your application. ideally, though, you want your shocks and struts to be adjustable, both in compression and rebound. These adjustments will give you the ability to fine-tune your shocks and struts to work with both your associated springs and your driving style.
There are also plenty of options for converting your suspension to a coil-over shock, which adds ride height to your available suspension adjustments. When converting to a coil-over, you’re very likely going to need to have some experience with welding, as you may need to add some new shock mounts to your car.
At this level of modification, you’re most likely looking for something outside of the standard offerings from most consumer brands. Luckily, there are a handful of companies that provide custom springs for any application, so long as you can provide accurate specifications and measurements to them. This will help you get the right spring for your application and driving style, though it will cost quite a bit more since these springs will be unique to you and your car, rather than a product that can be manufactured and sold on a large scale.
Just like when picking shocks and struts, you have the option of converting to a coil-over suspension. If this is the route you’re going, you’ll need to make sure the coil-over shocks and springs are chosen to work together. Since this option requires customization and modification of the shock mounts on your car and a hefty price tag for the parts themselves, you’ll want to make sure that you have your specifications right before you start.
If you’re at this level of modification, though, you probably know yourself, your car, and your needs pretty well.
For high-performance applications, a larger, static sway bar just won’t cut it anymore. You’re going to be adjusting the stiffness of the sway bar fairly often as track conditions change and your driving style adjusts, so having a large number of sway bars on hand in case you need to change to another size becomes prohibitive, both the cost and the sheer amount of storage you would need to accomplish this.
This is where an adjustable sway bar comes into play. Having an adjustable sway bar allows you to have one sway bar installed on your car and when you need it to be stiffer or softer, you only need to changing the settings by adjusting where the sway bar links connect to the sway bar itself. This saves time when needing to make an adjustment as well as space.
An adjustable sway bar is an expensive investment, but the ease of adjusting it and only needing one sway bar (rather on multiple sway bars in different sizes and their associated mounting hardware) more than makes up for the initial cost of this part.
Strut Tower Bars
At the dedicated track car level, a strut tower bar becomes more of a necessity than an option. You’ll also more than likely want and need a triangulated strut tower bar in order to help stiffen not only the left-right motion, but the forward-backward motion of the upper end of the suspension.
Polyurethane bushings are a necessity at this point. You need to remove as much flexing from your suspension as possible so that it can be as responsive as possible when cornering. This is at a minimum. Comfort and dealing with the possibility of squeaking is no longer a consideration.
I say that polyurethane is required at a minimum because there is a more extreme option that takes all possible flexibility out of the equation: metal bushings. These provide the stiffest option for suspension bushings. You won’t be dealing with any flexing in your suspension’s joints.
Adjustable Control Arms
If you’ve ever wanted complete control over your suspension’s geometry, adjustable control arms are exactly what you need.
They provide the ability to fine-tune the camber, toe, and caster of your wheels, in conjunction with all of the other adjustable parts of your suspension. They also give you the ability to compensate for geometry changes due to lowering your vehicle more than an inch or two with your spring and shock/strut combinations (especially a coil-over).
Adjustable Camber Plates
A camber plate replaces your strut mount, allowing you additional camber adjustment via the strut assembly. There’s not much to them, other than giving you additional adjustment of the existing suspension. When used with the other adjustable parts, it helps to provide ability to fine-tune your camber angle within a range from under the hood rather than having to make adjustments to the rest of your suspension.
Chassis Braces or Sub Frame Connectors
Chassis Braces or Sub Frame Connectors do one thing: they add stiffness to your car’s body. The unibody chassis makes building cars easier and more efficient. The main downside, at least when it comes to racing, is that the chassis loses some rigidity that a body-on-frame construction provides.
These are often bolted to the frame rails and subframe of your car, so they can be relatively easily be added or removed as your needs change.
While I can’t stress enough that the modifications you perform should be determined by what you plan on doing with your car, there are countless upgrades you can make to your suspension to fit just about any need you can think of. The modifications outlined above, though split between two polar opposites of options, can give you enough to work with to fit either plan or just about anything in-between.
When you’re modifying your car, not matter what you’re doing, be safe.