Coilover Preload: What is it and how to set it.

Coilover Preload: What is it and how to set it up.

In this article we go over the basics of pre-load, explain what it is and dive into how to set it up in most setups.

What is Preload? 

A long time ago coilover technology moved over to what is known as a pre-loaded coilover. This could be bc racing, d2 racing, truhart, godspeed, silver, buddy club, hks, kw and a hundred other brands all use the same mechanical engineering. This engineering essentially allows for adjustable ride height with a pre-set or preloaded coilover with a spring that doesnt get touched essentially. What this means is that the spring has a desired amount of pressure or tension on it.

So for instance negative preload would be where the spring can move around between its perch and top hat. Zero preload would be where the spring and perch are just touching and do not move around at all. And positive or preloaded spring is where you add anywhere from 2-5mm of tension, by adjusting the perch to squeeze or preload the spring.

What does this do exactly. Well one its loading some tension into the spring, so there is no movement of the spring or it popping out of place. As well when you raise or lower you arent changing preload or the gap between where the spring sits compressed and uncompressed. So this keeps it so you can adjust your ride height and maintain the exact same spring rate and function and overall sound and tightness of your suspension.

Also a small tip is if you want to shift your spring rate up some or down some just add or remove some preload. But do not get carried away. At first we suggest listening to what the manufacturer states to set the preload as. Or go for 5mm of positive preload for a rule of thumb.

How do you set Preload?

Well if the first section didnt have you running straight to your car to set it by the explination. Here is how you set it. Once you get it, just please be sure to link people to this article so we can help them as well get a little exposure for spreading the knowledge.

Two types of coilover setups.

1. The coilover and spring all in one setup. This setup is easiest to understand. You want to take the double spring perch and unlock it by reverse away from each other or unlocking the lower perch and bringing both perches down to give enough room to the spring so it can move up and down freely. But it doesnt need a lot. Then bring the perch/ lock ring thats right under the spring (the highest perch / lock ring) upward until it just touches the spring. And there is no motion. Then you will want to continue to raise the perch up 5mm more to set the pre-load generally which is for the front. Essentially squeezing the spring 5mm shorter.

You can also bring the lower lock ring right under the top one before doing this proceedure and then just as before you raise it 5mm away from the lower lock ring. Also just a note some lock ring tools are actually 5mm thick so you can just slide this lock ring tool right inside the gap of both perches and you are done. Thats it. From there you want to bring the lower lock up under the top lock ring and counter lock them towards each other. Ride height is then set via the lower shock perch where there is a 3rd ring at the very bottom right above the shock bracket. This unlocks and ride height is adjusted by dropping the shaft further down via twisting down or upward on the car.

Now onto the next style of setup.

2. The coilover and spring are seperate setup (usually the rears). You want to then set ride height via the spring length by adjusting the two lock rings up and down the spring collars. Once ride height is set. You have everything installed and you want to loosen the shock lock ring, you want to then drop the lower control arm by lengthening the shock, once you see a gap, reverse and go back to where you just snug the spring under the chassis to the car. And by snug we mean just touching to where there is no pressure. Then from there just measure the springs length and then add 5mm of positive pre-load to the spring. Then measure to confirm. From there you relock the shock perch and thats your setup.

A tip with the rear you might want to play with zero pre-load 5mm of preload or even some negative preload. This can allow a little more travel as well. Which can make a difference, as well the more pre-load the more oversteer the car can gain just by simple stiffening.

Why do I need to set Pre-Load?

A great reason to pay attention to preload is this could be where the extra noises are coming from when you install aftermarket coilovers.To get rid of them setting some positive preload will ensure the spring isnt moving around and banging about or popping in and out of place.

Proper spring function as well is another reason. This system is built to be preloaded. All oem suspensions have pre-load to some degree. But this is a tunable thing now that you understand it and just another tool in your belt when it comes to suspension tuning.

Rule of thumb, negative and zero preload = more suspension travel.
Positive pre-load, the spring is starting at a stiffer point in its travel. Quieter suspension, less play, less travel so heavy bumps could upset the car more. 

But keep in mind these are small incriments. We would also suggest using a digital caliper if you want to get really serious and brake this all down to as equal as possible on all 4 corners. Somewhat like ensuring that all 4 tires read exactly the same psi. The proper and equal effect from all 4 corners will make a difference.

Do my coilovers come preloaded from the factory?

This question gets asked to us all the time. As well we see a lot of people asking. Its basically like asking do you think people are always doing their job properly?  While assembling thousands of these, the basic job is assembly and usually stick into a box. During shipment anything can occur to the suspension as well. As well the seperate coil and spring setups, zero preload can be set off-car anyhow.

So, with the fact that setting the pre-load yourself and knowing it was done right and how, plus how quick and easy it is to do. It makes this a question that really doesnt matter to us. Even if the manufacrurer says they did or they do. Check and set your own pre-load yourself. Always.

Any EXTRA tips on setting pre-load?

Another thing to keep in mind as well is you may want to measure both left and right springs against one another in length and possibly go about adjusting preload slightly differently to get the springs to be the same length preloaded. So for example one spring is 1mm shorter, you would just add 1mm extra of pre-load to make both springs 140mm for example. Instead of adding 5mm of pre-load to both and having a spring that is 139mm and 140mm. This is just an example but something you can toss into your suspension setup when dialing your suspension. If its too much to think about and you dont feel like setting multiple settings of pre-load just stick with the above either way you are already so much farther ahead of the game just by having read and understand this article.

Hope this helps you all, please like, bookmark, subscribe and share this article if it helped you.

--SuspensionHOUSE Team