Suspension Tips


Okay, before you go getting all crazy and spending lots of money, let’s get one thing straight. No matter what you’re driving, you need to learn to drive it BEFORE you start tinkering with the suspension. If you have an older car, go ahead and take care of any maintenance issues like shocks, worn out bushings and things like that. Get a good set of tires. Get a good alignment (see the Alignment section). Get lots of seat time.

You see, the problem with suspension tuning is that it’s really easy to screw things up. The changes you make could make the car feel “better” than it was before, and could actually allow a novice driver to be faster with it, but it could still be very wrong and present you with a proverbial brick wall when you reach a certain point in the learning curve. And you wouldn’t know any better. Unless your car has a really poor suspension, you really should work on your driving skills first.

“Tune the driver, then tune the car.” Have I said it enough times?

Basics

Let’s say you’ve been autocrossing for a year or two and you’re feeling pretty confident in your driving skills. (or you’re just ignoring my always good advice and blindly throwing parts at the car trying to “make it faster”) You’ve had a lot of experienced people drive your car and you’ve given them all a run for their money… maybe even bested a few of them. What can you do to your suspension that will make your car a better autocross machine? I hope you’re not expecting a simple answer because their isn’t one. In addition to thinking about how much money you want to spend, you’ll need to consider things like whether you’ll be driving the car on the street (and where, and how much roughness you can tolerate) and whether you care what class your car will end up in if you compete with a club like the SCCA.

Remember that they call suspension tuning a “black art” for a reason. It’s very complicated, every car is different, and if that’s not enough every DRIVER is different. You may set things up a little differently than someone else due to your own personal driving style, I know I do. One big word of caution: Don’t expect every “set”, “kit” or part that you buy from a big name supplier to be right for you or your car just because the supplier’s reputation or name is all about “racing”. Most kits are designed for street use even if they call themselves “race” parts. Street use generally means “understeer” (an awful lot of aftermarket spring sets will give you a nice, low, understeering car) because it’s safe and puts less liability on the manufacturer. But it can also mean “ultra-stiff to make your car feel like a race car even when you’re driving it slow”. (this applies most often to swaybar sets) People tend to believe that stiffer and/or lower suspension always equates to better handling and it’s just not so. Balance is extremely important and “too stiff” is an easy mistake to make.

I’m just going to talk about some of the most common and simple suspension modifications in the order that you should consider them. Depending on what you drive, you may not need to do all of these things. You may not need to do ANY of them! But at least you’ll have a little idea of what to expect. My best advice is to consult with people who are very experienced with both autocrossing AND the suspension of YOUR car before making ANY decisions. Doing so can save you a lot of money, time and headaches. They may not be able to give you the recipe to make your car exactly what you want, but through their experience they can get you a lot closer than you’d get by throwing darts (and dollars) at your favorite parts catalog. Another good tip is to ask the hot-shoe drivers that you let drive you car to check your driving skills what they think is “wrong” with your car, they can usually offer good suggestions.

Shocks

Typically this is one of the first things to get changed on an autocross car, and a lot of people will argue that it is the most important thing other than the tires. If your aim is to compete in one of the SCCA stock classes, this is one of the few things that you CAN change and it will make a big difference. Like Pirelli used to say (yeah, they were talking about tires, but it’s still true): “Power is nothing without control.” This is what shocks give you.

You can spend a lot of money on good shocks, but you may not need to depending on what you drive and how far you’re going with suspension setup. If you’re using stock springs and are on a budget, you may be able to get away with a good stock replacement shock. (if your car has 40-60k miles on it, you may not even realize how poorly your old shocks perform until after you replace them) If you have a little more money to spend and are fortunate enough to have a car with good aftermarket support, adjustable shocks are a great way to go. Adjustables allow you to tune the characteristics of the shock to match your springs, your driving style and even the surface you’re driving on. If you have changed (or plan to change) to stiffer springs, your stock shocks probably won’t be able to handle the extra spring rate, so adjustables are a really good idea. The next step up the ladder are custom revalved shocks engineered specifically for your car and the way you drive it. Big bucks, but worth it if you have skills to back it up.

Disregarding the strange things people do with shocks in SCCA’s stock classes (when shocks are the only thing you’re allowed to change, creative people come up with interesting ways to modify shocks!), the primary purpose of a shock is to control the motion of the suspension and keep the tire in contact with the ground. They can also be adjusted to change the ” transitory” balance of the car. (the car’s tendency to under or oversteer as you enter or exit a turn rather than its “static” balance that is more a factor of the spring rates) Shocks need to be stiff enough to keep the spring from oscillating (which is why stock shocks don’t work well with stiffer aftermarket springs), but they CAN be too stiff. Set them too stiff and you’ll find yourself skittering across the top of the imperfections in the pavement (very few autocross sites or streets are anywhere near perfecltly smooth) because the shock isn’t allowing the suspension to do its job.

Sway Bars

Call them “sway bars”, “anti-sway bars” or “stabilizer bars” they are almost everyone’s favorite “best bang for your buck” suspension mod. Realistically, a carefully chosen set of bars really can be a great improvement and it’s not a bad place to begin with an otherwise stock suspension. Keep in mind that as your swaybars get stiffer, the car becomes less forgiving. It will be more responsive, but can be more difficult to control at the limit.

Adding “stiffness” and reducing body roll are secondary to the real purpose of a swaybar (on a sports car). What they are used for above all else is to balance the car’s handling. Most of the improvement that you can realize from changing swaybars does NOT have to come from adding a great deal of stiffness. You can achieve the balance that you’re after by merely changing either the front or the rear bar. Small changes in swaybar diameter can have large effects.

Remember, as mentioned above, just because someone sells a front and rear swaybar as a “set” does NOT make them correct for competition use! Do some research, find out what you’re getting before you get it and do some simple math to determine the potential effects. Two things determine the overall ” stiffness” of a swaybar: the length of the “arm” (the part that connects to the end link, most adjustable bars are adjusted by changing this length) and the diameter of the bar. The stiffness of the bar is a function of the 4th power of the diameter! This is why small changes in diameter can make a big difference.

If you plan to install stiffer springs, you don’t really need to install really stiff swaybars. You’ll get the roll stiffness you need from your springs (which is the more “correct” method) leaving the bars to fulfill their primary purpose of fine-tuning the handling balance. You’ll find that a lot of racers who have taken the time to carefully select their spring rates will often REMOVE one or both of their swaybars because they have achieved their desired balance without them. For a street car with spring rates that are “comfortable” for street use, you probably won’t want to eliminate your bars, but you may get by with stock bars if your spring rates are properly balanced.

Springs

Changing springs is a pretty simple operation on most cars if you have a good set of tools available. There are two ways to go. You can try to find a set of stock replacement springs, that is: springs that directly replace your stock springs, but are stiffer and shorter. Or you can spend more money and get a “coil-over” kit. Going with a coil-over usually gives you a threaded collar on the shock body for infinite ride height adjustment. (great for dialing in the exact height that you want, and also for balancing the corner weights) It also switches you to a standard diameter race spring, which gives you a wide variety of spring rates to choose from. For a lot of cars, a good aftermarket spring choice does not exist and you may be forced into using a custom coil-over setup.

There is one other option. It’s one that a lot of autocross purists shun, but I’ve found that there are plenty of “old timers” who aren’t afraid of it. I’m talking about cutting the length of your stock springs. (Hey! No flaming the tech writer!) Now, I would never, ever advocate just randomly hacking a coil or two off of a spring and hoping for the best. But I do know that you can calculate the rate of a spring based on its diameter, number of coils and the diameter of the wire it is wound from. If you want to try this, there are several things to keep in mind. First and foremost, don’t try to get extreme with this technique. If you just want a slightly lower car (maybe 1″ at most) and a slightly firmer ride, then there’s no harm in attempting this old trick. If you’re after more than that, consult your favorite aftermarket parts catalog. I wouldn’t cut more than a coil, if even that much from a spring. Note that the number of coils used in the calculation refers to “active coils”, that is, the number of coils that aren’t already compressed when the car is at rest. With that info, you can know with some degree of certainty what spring rate you will end up with after your cut. What you can’t calculate (or you probably could if you wanted to get really, really serious) is how much that cut is going to lower the car. Hint: It’s going to lower it significantly MORE than the free length that you’ve cut from the spring. Just two more thoughts on cutting springs and I’m done. Pay close attention to the ends of your springs and how they fit in your suspension. They may be “clocked” at the top and/or bottom so that cutting anything but a full coil would cause a fit problem. They may be flattened on the ends, which would shift cutting them correctly to someone with more equipment than a cutting wheel and more expertise than the average back-yard mechanic. And lastly, BE CONSERVATIVE. If you cut too much, you can’t put it back! You can always go back and make another cut if you didn’t cut enough. Proceed at your own risk.

Okay, those are your basic spring options. Now, what spring rates do you want? How stiff? How low? Tough questions. Depends a lot on suspension design, how heavy the car is, etc. But, do yourself a favor and DO YOUR HOMEWORK. Unless you’re deferring to a trusted autocross expert for a custom kit, KNOW what spring rates you’re getting and why. As mentioned above, a lot of aftermarket kits won’t be right for autocross. Springs being THE fundamental basis of your car’s handling balance, getting it wrong is difficult to overcome.

There isn’t much more I can say other than the simple warnings that “too low” and “too stiff” are very possible. Just as in the shocks discussion, you can get springs that are too stiff for street or autocross use. As for what “too low” is, it’s often more than just a ground clearance issue (which can be enough of a problem in itself). Unless you install a correctly designed coil-over kit or custom short-bodied shocks, installing shorter springs on your car WILL reduce the amount of available suspension travel. A lot of people don’t realize this and even people who do have been known to find themselves riding around on thier bump stops without even realizing it. Even if you’re not on the bumps at rest, if you only have an inch of suspension travel (unless you have insanely stiff springs), it’s pretty easy to get into the bump stop in the competition environment. What happens when you hit the bump stop? Well, the rubber cushions the blow a little, but once that rubber is compressed, your spring rate has gone from whatever your spring is to infinity. This can be bad. For instance, if it’s the rear that’s hitting the bump-stop, you could end up with snap-oversteer in the middle of a sweeper.

It’s also possible for “too low” to include problems like bump-steer that is caused by the steering tie-rods not being parallel with the ground. (as you lower the car, the outer ends of the tie-rods are effectively raised relative to the rest of the car) Another issue that appears more on front wheel drive cars is the angle of the drive axle bending the CV joints too far and causing them to fail prematurely and/or frequently.

As with everything else, choosing springs is a compromise. Choose carefully.

Bushings

By all means, replace any worn bushings! But, do carefully consider the purpose of your car before you spend a big wad on a complete polyurethane bushing set. There is no question that poly will tighten things up considerably giving you more control and quicker response. It will also give you a somewhat harsher ride that will vary in quality from one car to the next. If you’re concerned, try to find someone who has a car similar to yours who has already done it and take a ride in it.

What about Delrin or other “solid” bushing materials? Unless you’re building a track car, I wouldn’t recommend it. Delrin is very hard, might as well be brass or aluminum. Compliance is minimal, ride will be VERY harsh.

As I’ve mentioned several times, “too stiff” can easily be achieved. For the surfaces we autocross on and the streets we drive on, you need some compliance in your suspension to keep the tires in contact with the road. Bushings are a good place to allow some of that compliance to exist. If you DO opt to change bushings, be sure to change them ALL. Having bushings of varying hardness in your suspension can have strange effects.