things you should know about coilovers

Lately we have read quite a few incorrect comments online about suspension and coilovers, so we decided to write something about it.

Firstly, let’s go over a few suspension basics. There are a few popular suspension arraignments, mainly the Macphearson strut, double wishbone, multi link, and solid axle. Basically every modern car is going to be one of these designs, but that’s not what this post is about. Regardless of the layout, there will be a spring to support the weight of the car and resist roll and pitching movements, and then a damper, or shock absorber, to control the motion of the body and suspension. Without shocks, the body could oscillate freely on the springs and that would not be good.

When we talk about coilovers, we mostly mean an aftermarket suspension setup that usually has a variety of adjustments. However, as a general term, many oem suspension designs use “coilovers.” Coilover simply means a coil spring over the shock. Like this:

Here is a more adjustable version:

The second image is generally what people mean when they refer to “coilovers,” while the first image is often called a strut/shock and spring combo. They both are “coil over” suspension but we will stick to the common terms.

At a glance, we see a few differences. Firstly, the springs are different. The second set has smaller diameter springs, which are a standard size and can be interchanged easily with softer or stiffer parts. The shock bodies are also threaded, so the perches can be adjusted up and down.

What good does this do? Well, besides the obvious ability to adjust ride height, we can also change the springs, without changing the height. A helper spring (that second, smaller spring in the pictures), allows us to do both without having excessive preload or unseated springs at full droop. The other benefit of adjustable perches is the ability to corner balance the car.

Ideally, for the best handling, a car would have equal left to right weight distribution (unless you only wanted to, say, turn left). In reality, this is not the case. One side of the car is going to weigh more than the other because of things like drivetrain layout, the battery position, the driver, etc. If you are working on a race car, it is good to get this balance as close as possible as the car will be driven.

But most cars are not perfectly balanced, and even if one was, after just bolting up a set of suspension there would be some uneven preload from one corner to another. We check this by putting the car on four scales to measure the weight distribution, and then the suspension can be adjusted to fix an imbalance .This process is a key part in making a car handle well, and is a huge benefit of having an adjustable coilover suspension. With standard struts and springs, there isn’t much you can do (although moving weight around the car and shimming the top mounts are possibilities. Adjustable sleeves are also available for many standard struts).

The other side to this, is when an adjustable set of coilovers gets installed, but then is NOT corner balanced. The result will frequently be worse off balance than if just standard struts/springs were used, and potentially dangerous and inconsistent handling behavior. For anyone who buys a set of height adjustable coilover suspension, corner balancing should be considered mandatory. It is not “just for racing.” Some of the symptoms of very uneven corner balancing can include the following.

  • The car understeers turning one direction, but oversteers going the other.
  • Car prefers turning one direction only.
  • Even with a straight alignment there will be pulling to one side, especially under braking or acceleration.

That left-to right handling difference is the main reason for corner balancing, because we usually want a car to behave the same turning in either direction. Imagine that whenever you went around a right hand corner the car wanted snap around abruptly. That might be a good way to end up in the guardrail on the highway.

When it comes to height adjustment, you might notice there are some suspensions that only have adjustable spring perches, while others have a lower threaded mount, like this:

On the surface, it seems like a great idea- you can adjust the ride height without changing spring preload or changing the ratio of bump to droop travel. There are a few problems with this, though. The main issue is that the suspension can only compress so far before the tire runs into the body of the car. In reality, if you take one of those super adjustable coilover sets, and lower the height way down using the lower mount, yes, the shock will still have the original amount of bump travel, but the tire will probably end up hitting the fender, the liner, or maybe a wiring harness, The axles might contact the frame, and all sorts of other bad things can/will happen. MotoIQ has a good article about such a car here, and here is a wiring harness that was chewed up from tire contact:

So unless you are ready to cut apart the car, relocate things like wiring harnesses, and can fix the suspension geometry issues caused by over-lowering, that “independent ride height adjustable” set of coilovers might not actually offer any benefits. A well designed set of suspension will run out of shock travel just before the tire hits anything, and they also tend to have more overall travel, which is a good thing for both ride comfort and handling. The main benefit of the double adjustable “feature” is that it makes it easier for a suspension company to use the same shock for a lot of different cars, without having to put much thought into appropriate travel or damping specific for that vehicle. When installing a set of this type of coilover, it is a very good idea to remove a spring and jack up the suspension all the way to the top of the travel to insure the tire is not going to rub.

The next thing found on many coilovers is damping adjustment. Depending on the shock, this can be really useful. How the damping should work depends on quite a few things: the weight of the car, the unspring weight, the tires, the spring rate, the road/track condition, and what the driver likes. So there is really no one perfect damping curve for any given car and suspension setup. The best we can hope for is to have something the driver and passengers like and results in better lap times. An adjustment knob or two can really help fine tune both ride and handling. Damping adjustment will also allow a wider range of spring rates to be used before re-valving is necessary. HOWEVER, the person turning the knobs needs to know what they are doing, and the knobs need to do what they are supposed to.

There are many good suspensions that do not have damping adjustment, that are well liked and perform well under a wide variety of conditions.. Those yellow struts and springs in the first picture, which are Bilsteins tuned by Racecomp Engineering with their matching springs, are a good example. No adjustments- just install and enjoy. On the other hand, there are many suspensions with a lot of knobs that do not work well. A good rule of thumb is that the cheaper a shock is, the fewer knobs it should have. Don’t get fooled by the $1000-1500 double-adjustable coilovers; when they wind up on a dyno it’s not uncommon for those knobs to not do what they are supposed to, and the shocks will often not match. So even though the are set at the same “click,” the left and right dampers are behaving differently.

Like we mentioned, the damping required depends on a variety of things, including the spring. With stock/worn out shocks, installing lower and stiffer aftermarket springs is usually not ideal. The right amount of damping for good handling is usually higher than what is best for ride comfort, so while stiffer springs are usually better for performance, the resulting under-damped condition is not. Aftermarket lowering springs are cheap on their own, but in many cases should be paired with a better shock.

I believe that covers most of the basic differences between what are called struts and springs, and coilovers. For someone looking to change their suspension, it’s important to consider how it is going to be used. For a daily driven car, a good strut and spring combo will often be more durable, more comfortable, and possibly less expensive. When handling is the priority, the additionally adjustments of some coilover systems can be worthwhile, but they come at a cost. Coilovers that ride well on the street, perform on the track, and will remain trouble free for years exist, but they cost more money. It is also important to consider that the setup and alignment for coilovers is more involved. A standard alignment shop will often not know what to do so it is important to find a place that can properly align and corner balance coilover suspension.

I suppose next time we can talk a little more about damping and some suspension brands.. But for a short list of stuff that is both good and fairly inexpensive, start with KW, Bilstein, Koni, and AST. There are also companies that specialize in certain makes and have their own version of products, like the previously mentioned Racecomp Engineering. Almost everything they offer is based on a KW or Bilstein product (and we used some of their photos for this article).

 

Things you should know about coolant

This will be the first winter my car will spend in a cold climate in a few years, and I realized that my cooling system is in danger of freezing if I don’t add some anti-freeze. This brought me to look up the ideal water to coolant for cold weather usage, and then lead to much more research on cooling systems and how coolant works. I thought it might be a good idea to share results on how the boiling point, freezing point, and heat transfer ability of coolant change depending on the mixture. Also, this would have been easier if my thermodynamics textbook wasn’t in a storage unit 1000 miles away.

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Things you should know about suspension bushings

Have you noticed how quiet and smooth most modern cars feel to something a few years older? Drivers are being increasingly isolated from the road with soft rubber, liquid filled mounts, and sound deadening. This is done to reduce what’s called noise, vibration, and harshness, or NVH, and the downside is often a reduction in handling performance and response. The enthusiast driver who actually wants to feel the road is stuck with a numb, disconnected feeling, sofa on wheels.

The nice thing is that there is a fairly easy and inexpensive way to regain some control and performance, in the form of replacement suspension bushings. Bushings are all the little rubber parts in our suspension that absorb vibrations and allow motion. Changing out these tiny, often overlooked bits makes a difference in a number of ways.


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Things you should know about anti-Lag

Anti-lag is a very interesting technology that came about in the 1980s when rally cars started to use turbochargers. To fully explain it, first I have to explain what lag is, and why it occurs.

An engine is an air pump, and the more air that goes into a motor, the more power it will make. The primary factors that determine how much air is flowing through an engine are displacement and RPM (although in reality it is a little more complicated). As engine speed increases, so does the amount of air that goes through the motor. The same goes for displacement: a bigger engine moves more air and makes more power. Most of the time, we don’t have much room to increase displacement or revs. This is where forced induction, and the turbocharger comes in.

A turbocharger is a compressor spun by exhaust gasses. The purpose is to both reclaim some of the lost energy from the exhaust, increasing efficiency, and to increase the pressure of the intake air. Forcing more air (and the corresponding extra fuel) into the engine means that you can make more power with less displacement.

The downside is that it takes some time for the turbo to get going, especially when you are using a large turbo to make a lot of power out of a small displacement engine. Until the engine is moving enough air to spin the turbo, you’re stuck with a low displacement motor with low compression and no boost. This is called turbo-lag. In some cases you can compensate for the lag by increasing the revs to give you a larger in-boost powerband, but you still have that dead spot at low revs and higher engine speeds mean much higher stress on the engine components. Additionally, many racing classes require the use of an intake restriction, which limits the amount of air that can be drawn in, and therefore limits the maximum power and useful rpm range. These inlet restrictors will actually cause lag on all their own due to the fact that the turbo has to draw air through a smaller size hole.

The most simple form of anti-lag, used in the 80s, was to never lift off the throttle. This kept air going through the engine and the turbo spinning, but resulted in significant wear on the brakes and transmission, especially given that some rally cars were making over 600hp. Soon, systems were created to keep the turbo on boost even when the throttle was lifted.

To generate the low end power and response required by a rally car, it’s necessary to have the turbo spinning as soon as possible, creating boost before the driver actually presses the throttle. The simple way to do this is to keep the throttle partially open so plenty of air is going through the motor, dump a bunch of fuel, and then wait until the super-rich air fuel mixture is on the way out the cylinder before igniting it. Instead of having the combustion event force the piston down to make power, it explodes going into the turbo, creating boost.

As you might imagine, having the combustion occur in the exhaust is bad for the exhaust valves, exhaust manifold, turbocharger, and anything else in the vicinity like an EGT or O2 sensor. It sounds a little something like this:

The “add fuel, retard timing” form of anti-lag was used in the late-80s to early 90s, at which point rally teams began to come up with more sophisticated methods. Bypassing the combustion chamber entirely and injection air straight into the exhaust manifold allowed more boost at lower rpm. The Mitsubishi EVO VI, for example, came stock with an air injection anti-lag system that could be enabled simply by modifying the ecu. Then Prodrive came up with an even more complex system:

That little doohickey attached to the up-pipe is known as “the rocket.” A canister connected to the charge pipes stores pressurized air, and when the throttle is closed an air/fuel mixture is ignited in the rocket, spooling the turbo. This allows the 2.0 Subaru WRC motor to create useful boost (and 200hp) at the idle speed of 2000 rpm. By 2500 rpm the manifold pressure is 30psi, and reaches a maximum of 45psi by 3000 rpm. Peak torque is 520 lb-ft, and a little over 300hp is available from 3000 to the 7500 rpm redline. The important part about this system is how precisely it can control turbo speed and boost. By using a turbo speed sensor, this system is much more efficient, and allows more manifold pressure at lower revs with less wear to the exhaust components and turbo.

Things you should know about ride height

It’s a pretty common train of thought that lowering a car lowers the center of gravity and improves handling. Unfortunately that is not the whole story. When it comes to handling performance, keeping the tire in optimum contact with the road is the most important consideration. That means that the tread is flat on the ground, and has the most consistent contact with the ground possible. So with that said, lets go over a few things that happen with the car is too low.

The first problem that occurs with a lowered car is a reduction in bump travel. If you don’t have enough bump travel, you’ll be hitting the bump stops or even riding on them all the time. That takes away from the struts and springs being able to do their job, and creates sudden loading increases to the tire. Remember what I said about keeping consistent contact with the ground? Well hitting the bump stops is not consistent contact. This sudden bump in load drastically reduces grip. If your car is too low, you may feel this as a skipping or unsteady feeling while cornering over bumps, or perhaps just a general lack of grip. It will certainly make your laptimes significantly slower.

But wait, there’s more!

There’s something called a roll center. The roll center is a point the body of the car tries to roll about. Or, more specifically, the point the center of gravity tries to roll about. So if you increase the distance between the roll center and center of gravity, you increase the roll couple, and therefore increase body roll given the same lateral force. So that’s fun, right? Generally speaking, lowering a car lowers the roll center. All else the same, this INCREASES body roll, (although I’ll admit some of the extra roll will be offset by the lower center of gravity). With this little tidbit, we’ll move onto what’s called the camber curve.

Remember that part I said about keeping the tread flat on the ground? That’s where the alignment and camber curve come in. As the suspension moves through it’s travel, the alignment changes. Ideally, negative camber will increase with bump and toe will experience little to no change. With double wishbones and multi-link suspension, this is pretty common. Camber gain is important because in a corner the car leans over and the outer tire leans over. Using the suspension geometry to lean the tire inward with bump keeps the contact patch flat with the ground and increases grip. Most suspension geometry does not do this well enough, especially when the car has been lowered. Macpherson strut systems (used on subarus and evos for example), will lean the tire in a bit at first, and then lean the tire outward. That means the tire is riding on the outside edge and sidewall. Guess what that does for grip?

So, in conclusion, lowering your car too much will cause you to ride the bump stops, increase body roll, and reduce the amount of tread in contact with the road. Any of those three are cause for concern when lowering a car. Most of the time, when a car is lowered, all three come into play. And that’s just not functional.