Setting Up Coilovers

Setting Up Coilover Springs

Getting your springs set up correctly is a critical factor in your ride quality. Springs are the first step in tuning a vehicle's suspension system. The spring's job is to properly support the weight of the vehicle and its loads, the shock or damper is used to control the movement.

There are two basic types of coilover spring setups, Single Rate and Dual rate, single rate utilizes a single spring to support the weight of the vehicle and has a single linear force curve, while most “bolt-on” shocks utilize a single rate system, Dual rate utilizes a pair of springs to work together in a combined rate, the dual rate can generate greater bottoming resistance when utilizing the cross over rings, creating a two-stage force curve depending on rate and cross over position.

What Springs are on my ADS Coil Overs?

If you are trying to determine what length rate and inside diameter spring you have on your coil over it can be found on the spring itself, we only use Eibach springs on our coilovers normally they are a silver color, and there will be a black part number embossed on the spring normally centered on one of the coils. The part number is broken up into 3 parts, the first part is the free length. For example: 1400.XXX.XXXXS; 1400 represents 14.00”. The second part of the number indicates the inside diameter of the spring (in some cases the outside diameter). For part number XXXX.300.XXXXS, this would be a 3.00” ID spring. The last portion will be the rate in LBS/IN. Part number XXX.XXX.0650S, would have a 650 lb/in spring rate. The S calls out the color code of the spring, which in this case would be silver. To sum it all up a 1400.300.0650S would be a 14” long, 3.0” ID, and 650 lb/in silver coil spring. If you need particular information on your spring, Eibach lists every spring spec sheet at www.eibach.com under the race spring tab.

Setting Up Single Spring Coilovers

Single spring Coilovers are simple to set up as there normally aren’t too many options. Single spring shocks are normally 8 inches of travel or less. Larger travel shocks can also have one spring but dual rate is the preferred option because you can engage only the lower spring to increase your spring rate before fully bottoming out. Running soft springs will always give you the plushest ride but sometimes there’s a limit to how soft of a spring you can fit on a small coil over. Let’s go through some numbers on what our options are for different spring rates while maintaining ride height or lifting it.

Let’s say I have a long travel shock with 8 inches of travel and an 1800.300.0650s spring. When the shock is fully extended the spring nut is up touching the top cap, but the spring is at 17 inches. This means we now have exactly 1 inch of actual preload. Going on Eibach’s website and searching the spring I can see that it only has 9.02 inches of travel. To check if I can add any extra preload to lift the truck I’ll add the 8 inches of travel to the 1 inch of actual preload, I get exactly 9 inches. This means we are .02 inches from the spring coil binding when the shock is fully compressed. In this situation, I cannot add any more preload to lift my vehicle. Now if we look at an 1800.300.0500s spring on Eibach.com we can see that it has 9.57 inches of travel that will let us add more preload but it’s a softer spring so we need to see if it can also make our ride height the same. For this, we need to figure out exactly how much force the shock sees. The truck weighs 4500 lbs. but the shock being mounted on a control arm makes it have a motion ratio. We need to get out our measuring tape and take one measurement at ride height, the spring's length. Let’s say it’s 13 inches with the full weight of the vehicle on it. We already know the spring was at 17 inches fully extended with 8 inches of travel. Seeing that it compressed 4 inches we can identify the shock has 4 inches of up travel and 4 inches of down. Now we can get the corner force. The spring is an 18-inch-long spring but it’s been compressed a total of 5 inches because we have that original inch of actual preload. We also know the spring has a rate of 650 pounds per inch, so multiplying the spring rate (650lb) by how much has been compressed (5”) gives us 3250 pounds per corner. Now we can see if the 500-pound will work, take the corner force, and divide it by the new spring rate to see how much actual preload a 500-pound spring needs to keep the same ride height. 3250/500=6.5 inches now subtract the 4 inches of down travel because we like the ride height, and we can see that were left with 2.5 inches. This means the spring needs to have 2.5 inches of actual preload. Using the 2.5 and adding our 8 inches of travel we do not know the spring will be compressed a total of 10.5 inches when the shocks are fully compressed. We can check if it will coil bind by comparing the spring specs, sadly it only can be compressed a total of 9.57 inches and not 10.5. Now we know that the spring will not work. We can run through a couple of different springs and see if we can go softer but this setup with 1 inch of actual preload is set up nicely. This example was made to show coil binding and the limitations of a small shock spring, if the shock's actual preload is 0 or less, then it's highly recommended to drop the spring rate and add more preload to it so it can get you at the same ride height.

Corner Force = (Spring Rate) * (Down Travel + Actual Preload)

Setting Up Dual Spring Coilovers

If your vehicle has dual springs on it already, we can use a measuring tape to find the force that the shock sees and compare how different springs can get us a softer ride, firmer secondary rate, and the same ride height. If the part numbers on the springs are eligible and we have a measuring tape, we can calculate all the info with these equations. Keep in mind this only works at ride height and having all tools and any additional weight added to the vehicle.

As an example, I’ll be using a 14” coil over with a 1400.300.0200s spring over a 1600.300.0200s. The lower spring should be 2 inches longer than your shocks travel and the upper can be the same or 2 inches longer also. Keep in mind that the lower spring should have a heavier spring rate or the same as your upper. First, I am going to measure my springs and find out how much down travel there is to calculate the cornerforce. It's important to verify that the slider is not already sitting on the jam nuts at ride height these numbers will be off. I already know the lengths of my spring and their rates so I will measure the combined length of my spring at ride height with my truck fully loaded. It's very important that all tools, fuel, or any additional weight that goes in the vehicle is in there before starting. My overall length of both springs is 24.5 but I measured with the slider on there, so I can just subtract its thickness and see that they are at 24 inches. I know I have a 14” over a 16” spring and their combined length without load is 30”. That lets me know they are compressed 6 inches. The last measurement we need is how much shaft is exposed, I have 8” of the shaft showing on a 14” coil over so now I know I have 6” of down travel. Comparing my down travel to how much the springs are compressed I can see that they are the same, this means I have 0” of actual preload.

Corner Force = (Combined Spring Rate) * (Down Travel + Actual Preload)

Combined Spring Rate = (Upper Spring Rate * Lower Spring Rate)/(Upper Spring Rate + Lower Spring Rate)

Upper spring = 14” x 200lb

Lower spring = 16” x 200lb

Actual preload = 0”

Up travel = 8”

Down travel = 6”

Combined spring length at ride height = 24”

Now it’s time to run through numbers and see what options I have.

Using the equation for my combined spring rate (200*200)/(200+200)=100. This means my shock has one long 100lb spring until the slider hits the jam nuts. When the shock compresses the slider will keep moving up until the jam nuts stop it. As soon as that happens it engages the lower 200-pound spring doubling the spring rate. This increase in spring rate can increase bottoming resistance.

The height of the Jam nuts is going to affect when that spring rate increase happens. More on that soon. Next, we need the Corner force (100lb)*(6”+0”) = 600 lbs this means each shock needs 600 lbs of spring rate to keep the truck at ride height.

I do not have bypasses so I will be trying to get 2 inches of preload, if we were running a secondary bypass shock, I would shoot for around 3 inches of actual preload. We need to see what the goal combined rate is with the extra 2 inches as shown here 600lb/(6” of down travel +2” of preload) = 75.

Now we can play with different combed spring rates and see what will get us at the same ride height or close. 100–200-pound separation from the upper to the lower is another good number to shoot for.

So, I think I want to try a 150 over a 250 spring, (150*250)/(150+250)= 93.75lbs and that’s firmer than our goal but we can see how much preload it would take to get our ride height. (600lb Corner force / 93.75 Combined spring rate) -6” of down travel = .4 inches of preload, so I know it's better but let's drop to a 100lb over 200lb. (100*200)/(100+300)= 66.66 combined spring rate, this is soft but let's see how much preload I would need. (600/66.66)-6= 3 inches of preload required for keeping my ride height the same. Perfect for a bypass application but not mine. A 100 over a 250 gets me a 71.42 combined spring rate and trying that we get (600/71.42)-6 = 2.4. I like the 2.4 inches of preload because I have a decent sway bar and bump stops so I'll get a 1600.300.0100s and a 1600.300.0250s spring. I decided to go longer on the upper so I could keep the spring nut more toward the top cap. Now I can decide how to set my jam nuts.

Setting the jam nuts on your dual-rate coilovers can help tune and add an extra zone of stiffness before bottoming out or hitting a bump stop. Let’s say that I have 2-inch travel bump stops and 8 inches of up travel on my shock. I want my spring to engage 1-2 inches before my bump stop does so I’m not always hitting the slider on small bumps or having the lower spring engage at the same time as the bumps because it would be too harsh. The goal will be to have it engage at 4 inches of shaft travel, this means the shock will compress an additional 4 inches from ride height and that’s where I want it to engage. The slider does not move proportionally to the shaft because the springs split the load, this means we need to set the jam nuts about 2 inches above the slider to make it engage at 4 inches of travel. After a good test drive, I can see if I’m barely using my bump stops or just blowing through them. If I’m not using all my travel I could raise the jam nuts to 2.5 inches above the slider or bring it closer if I’m hitting the bump stops too much. When setting a slider height it's always good to double-check if a spring will coil bind when the shocks are fully compressed. This can be done by checking out Eibach.com to see what height their spring blocks out. If it does coil bind while driving the spring will lose its spring rate and make the truck will lose ride height, so it’s very important to prevent this from happening.

If your Coilover is a dual rate, then there are some adjustments to make with the jam nuts to help dial in your ride. A lot of the time when a vehicle is bottoming out during high shaft speed bumps people jump to the conclusion that they need heavier springs. In most cases that should be fixed with a shock’s valving unless the vehicle is bottoming out during low shaft speed situations. If a coil over has dual springs, then adjusting the jam nuts or even swapping out the lower spring would be first step to keep it from bottoming out during those low shaft speed moments. Before we dive into how to set up and calculate your ideal springs, please make sure these phrases below are understood.

High shaft speed: High shaft speed is when the shock compresses extremely fast. For example, hitting a curb head-on with some decent speed.

Low shaft speed: Low shaft speed happens during dips or G-outs. For example, coming down a hill transition. You should feel the shocks slowly compress as you get sucked into the seat.

Coil binding: Coil binding is when a spring hits its maximum fully compressed length. This is very important because if a spring does this then the shock will instantly stop moving and even damage the spring’s shape-memory and make it lose its spring rate.

Actual preload: A shock’s actual preload is how much the springs are compressed when the shock is at full extension. Not to be confused with the measurement between the top cap and the spring nut.