Coilovers Setup got Explained

Basically, Coilovers integrate the springs which support the weight of your vehicle and the shocks which absorb the forces as you drive. Coilover shocks save space by combining these two integral parts of your suspension into one.

A coilover shock will support the weight of your vehicle so it is important to select the correct spring rate to ensure proper the proper ride. Equally as important is the shock valving which goes hand in hand with the spring rate to give you the smoothest ride in even the harshest of terrain.

There is nothing particularly magical about coilover shocks - their use requires strict attention to mounting geometry, spring rates, and shock valving the same as any other system.

Don't worry if not all of those statements make complete sense to you at this stage - they will by the end. Let's go over the different types of coilovers and then dig in to the parts and their functions.

Most coilover shocks will fall into one of the following three categories:

• Remote reservoir

• Piggyback

• Emulsion

Remote Reservoir coilover shocks are the most common. They are nitrogen-charged mono-tube shocks and are commonly available with up to 18" of travel. They use a remote reservoir to house the nitrogen charge and floating piston, allowing the use of a shorter tube than would otherwise be necessary. The reservoir is connected to the pressure tube with a short, flexible hydraulic hose. Swivel fittings and different length hoses are easily installed providing flexible mounting options for the reservoir. Depending on the position of the piston in its travel, there will also be a certain amount of oil in the remote reservoir. Theoretically, depending on the mounting location of the remote reservoir, this could provide a slightly improved cooling capability - but this is not the primary purpose of the remote reservoir. Then again, if the reservoir is mounted too close to a heat source (engine, exhaust) this could cause a detriment to cooling

A piggyback coilover shock is identical to a remote reservoir shock except that the reservoir, instead of being attached to the shock with a flexible hydraulic hose, is mounted directly on the shock with a bracket that incorporates the necessary hydraulic passage between the cylinder and the reservoir. Because of this they can be more of a challenge to fit. Technically, both a remote reservoir shock and a piggyback shock can be mounted upside down and still work - although there's no reason to do so and every reason not to, as the reservoirs would be very vulnerable in that position

An emulsion coilover shock has no reservoir and no floating piston. It is still a gas-charged mono-tube shock, but the nitrogen charge is contained in the pressure tube along with the oil in an emulsion. Less resistant to aeration, foaming, and fade than the external reservoir styles, they are best suited to light weight and / or low-speed use. They are more compact and therefore easier to fit than the other styles. Also more economical than the other styles, they are usually adequate for rockcrawling use. An emulsion shock can only be mounted right side up

Coliover Setup Guidelines

There are a great number of tuning and adjustment factors to consider when using coilovers, which we shall discuss in detail shortly.

For now, it is sufficient to understand that a coilover shock with springs mounted functions as a unit that provides both springing and damping. One end of the shock has a fixed, integrated spring seat and is mounted to the axle or suspension. The other end, which incorporates an adjustable upper spring seat, is mounted to the chassis.

The springs are installed over the body and shaft of the shock between the fixed lower spring seat and the adjustable upper spring seat. Springs of many different lengths and rates can be accommodated, which combined with the ability to alter the shock's internal valving, gives a wide range of tuneability.

Since the shocks have a great deal of travel (to permit the large amounts of wheel travel needed for offroad use) a great deal of spring travel is also required to prevent the springs from bottoming before the shock. In order to achieve the necessary spring travel a very long spring is required. However, because there is a practical limit to how long a spring can be made before it will tend to buckle, multiple springs are stacked in series on the shock (one on top of the other) in order to achieve the required spring length.

The most common configuration consists of two springs stacked together in series, and is called a "dual-rate" system as frequently the two springs have different rates.

The upper spring is called the "tender" spring or coil, and the bottom spring is called the "main" spring or coil. (From this point forward I shall use the terms "spring" and "coil" interchangeably.) A nylon sleeve, known as the dual-rate slider (DRS), "floats" on the body of the shock between the two springs. As the springs compress and rebound, the dual-rate slider slides up and down the shock body. When multiple springs are stacked in series in this manner, the result is a variable spring rate that begins as the (normally softer) rate of the combined springs and progresses to the (normally stiffer) rate of just the main spring. The rate is initially soft because both springs are compressing together. When the springs compress far enough, the DRS slides up until it hits the stop ring and is prevented from sliding further. At this point, the dual rate slider effectively becomes the upper spring seat, locking out the upper spring. From this point, remaining spring travel occurs at the rate of the lower, main spring alone. We shall discuss dual-rate systems in great deal, including relevant formulae later. For now it is sufficient to know that stacking multiple springs gives us the required spring length and allows us to use a softer initial spring rate that transitions to a firmer rate at some point in the suspension's travel.

With a basic grasp of how they operate, let's now examine the coilover shock and it components in detail.

Great. So how do we go about getting the best performance from our coilover shocks? How do we most closely approach that magical balance between ride and handling, between firm and soft suspension? What are our goals?

The Seven Goals of Suspension Design Designing suspension is a matter of achieving the best balance between these often competing goals:

1. Desired suspension frequency

2. Desired suspension height

3. Desired ride comfort

4. Acceptable roll resistance

5. Desired flexibility*

6. Matched wheel, spring, and shock travel

7. Desired ride height

(* by flexibility we mean the ability of the rig to apply enough force (weight) at each corner to flex / articulate the suspension enough to make use of all the wheel travel (bump) available. If springs are too stiff, wheel will stuff, then start lifting corner before full bump is reached)

While avoiding

1. Bottoming out the shocks

2. Coil-binding the springs

3. Springs coming loose and falling out on full shock extension

Before we design our coilover system, though, the following preliminary work must be completed. With the exception of the last point, for the purposes of this article, I shall assume these have all been completed:

• Chassis fabricated

• Tire size decided

• Multi-link suspension designed and built

• Ride height decided

• Max theoretical wheel travel calculated

• Coilover mounting geometry decided and checked for clearances between shock / spring and tires / chassis

With all that done, we have the information required to begin our coilover system. The first steps are:

Step 1: Measure Your Compressed Lengths

All measurements should be performed with the springs removed and the vehicle safely supported.

With performance off-road shocks, your compression stroke is always your limiting factor. To measure your compressed lengths, move your suspension to the full compression position. For solid axle vehicles this will need to be done in the horizontal, right tuck, and left tuck positions. Your limiting factor could be the differential hitting the oil pan, the tires hitting your fenders, your driveshaft angle, cv-shaft angle (IFS), or your suspension binding. In any case, you will want to find the minimum distance from your upper to your lower shock mounts at any position.

If you haven't placed your upper or lower shock mounts yet, then focus on putting your upper shock mounts up as high as you can put them. The higher your upper shock mounts are, the more stability you will have and the larger the shock you will be able to fit. The rule of thumb with shocks is that you always want to go with the largest shock you can fit because you can always limit your down travel with limit straps and you gain stability, more oil capacity for better cooling, more shaft overlap at full extension, and room for growth if you ever choose to go bigger down the road.

Step 2: Measure Your Extended Lengths

This is also a great time to measure for limit straps. Keep in mind that all limit straps stretch by design and you will need to include that stretch in your measurements so be sure to ask the manufacturer or your dealer for this information. It is a good idea to limit your suspension travel at about 1" before full extension on 14" and smaller shocks and 2" for 16" and larger shocks.

*Important!Never order new shocks based on the measurements of your existing shocks. OEM and generic aftermarket shocks have much smaller internal components and are thus able to get more travel out of a smaller shock body. When ordering performance shocks, it is critical that you measure the dimensions of the vehicle only.

Step 3: Determine the Appropriate Shock Size

When choosing your shock size you always want to go with the largest shock you can fit on the vehicle that will still let your suspension reach full compression. Even if your suspension only cycles 12”, if you can fit a 14” or even a 16" shock, then that is what you should shoot for.

In some cases, there may not be a shock available with both the compressed and extended length you need so you will have to decide on which dimension to sacrifice or consider moving your shock mounts. In general, for a rock crawler it is far more important to have up-travel (shorter shock) whereas a mud/desert truck might be better suited for more down-travel (larger shock).

Finally, you never want to bottom out on your shocks or over extend them so leave a bit of margin in your calculations and make sure to always run an external bump stop and limiting straps.

Never Order New Shocks Based On Your Current Shock Lengths

A very common mistake that people make is ordering new shocks based on measurements taken from of their existing shocks. High performance shocks have much larger parts that take up more space inside of the shock body and reduce the amount of travel available for its size.

The photo to the right shows three popular 12" travel shocks all in their full compression position. The King shock is several inches longer than the Bilstein which is a couple inches larger than the generic shock. If you order a King shock to replace a generic shock based on its size or travel, it will significantly limit your suspension's up-travel, down-travel, and/or overall travel.

Always order your new shocks based on measurements taken from the vehicle, never from the existing shocks.

Shock Cylinder Size (2.0 / 2.5 / 3.0)

While selecting the proper shock length is directly related to the suspension travel of the vehicle, cylinder size is strictly related to the amount of energy the shock needs to absorb and dissipate. It is common to hear vendors say "just go with the biggest shock you can afford" but that doesn't mean a larger shock will always give you better performance. In fact, it is just as bad to have too small of a shock as it is too have too big of a shock.

Many factors need to be considered when choosing a shock cylinder size, but it more or less comes down to the weight of the vehicle and how it is used. Light vehicles need less shock while heavier vehicles need more shock. Vehicles used for slow movements like rock crawlers need less shock while desert racers need more. The table below is a list of typical shock sizes for common vehicle types.

The above recommendations are posted to give you a rough idea of how shock cylinder size compares to common vehicle types and applications. Hydraulic bump stops are a critical component in any performance suspension system and are highly recommended. Bypass shocks are required for advanced suspension tuning and to provide additional energy absorption for high speeds and long distance runs. If you are unsure of what combination you need for your vehicle, please consult an expert so they can point you to the right selection

The next step is to select some preliminary spring rates. There are many factors that go into any suspension design intended to satisfy the seven goals mentioned before, including: spring rates, shock length, spring length, shock / spring mounting geometry, link geometry, shock valving, and the use of tools such as bumpstops, limit straps, and anti-roll bars. Spring rate, or how stiff the spring is, will affect all seven of the suspension design goals, so picking spring rates seems a logical place to start. This is normally what we do. But first, there is one very, very important point I wish to make, and that is:

The problem with spring rate is that so many people treat it as it was the goal, instead of a necessary calculation to arrive at the seven goals stated above. Keep in mind that spring rate selection is a means to an end, not the end itself.

Spring Load Rate Calculations:

Incorrect springs, like the examples shown in the right, will not only result in bad performance, but can also result in damage to the shock if not fixed. In many cases, if the springs are not too far off, only one spring needs to be changed as the other can be moved up or down.

The goal for most performance applications is a combination of springs that are as light as possible, yet strong enough to support the vehicle at the ride height that you want without needing more than a few inches of preload

Step 1: Calculate Your Effective Coilover Load

Measure the Height of the Lower Springs Under Load

While you may have calculated your corner weight , the real world always ends up being a little different. Luckily, the easiest way to accurately determine your ideal spring rates is to calculate them based on your existing springs.

With the vehicle sitting under its own weight, and the preload adjusted to give you at least an inch or two of shaft exposed, measure the current height of the lower spring to within a quarter of an inch.

The bottom spring is the one measured because it is always supporting the entire corner weight of the vehicle whereas the upper spring can be limited by the stop nuts.

*New coilovers have a tendency to stick in certain positions, particularly on lighter vehicles. If this is the case, cycle the suspension in both directions and do you best to find the equilibrium point before taking your measurement.

Determine Your Lower Spring Specifications The other information needed to calculate your effective sprung corner weight is the free height of the lowest coil and its spring rate (measured in lbs.).

Most new coilover springs will have this information printed on the side of the coil. If not, you may need to remove the coil from the shock and look for the spring rate engraved on the top of the spring and then measure the free length with a tape measure.

Spring specs include the inner diameter (2.5, 3.0, 3.75), height (4 to 26) and spring rate (80 to 1000).

Calculate The Effective Sprung Corner Weight To compute the effective corner weight, you start by finding how much the lowest spring compresses under the weight of the vehicle. This is done by subtracting the measured height of the spring from the free height. Then, to calculate the effective corner load, you multiply the compression distance by the spring rate.

Example:

A 2.5x14x250 lbs. lower spring with a 10" measured height under load.

[14" (Free Height)-10" (Measured Height)] x [250 Lbs. (Spring Rate)] = [ 4" ] x [ 250 lbs. ] = 1,000 lbs.

Step 2: Calculate the Required Spring Rate

Determine The Desired Ride Height

With the effective corner weight now known, the next step is to find how much the correct springs need to squat in order to settle the vehicle at or slightly below your desired ride height. At this point you should have already decided where along the coilover's travel you want the vehicle to settle (either a known position or a set distance up or down from where the vehicle sits now). The measurement used for this calculation needs to be the number of inches of exposed shaft desired at ride height.

Calculate the Required Spring Squat

Finding the required distance that the spring(s) need to squat in order to settle at the desired ride height is easy, just subtract the desired ride height from the overall travel of the coilover.

Example:

A 14" Coilover with a 5" ride height.

[14" (Coilover Travel)] - [5" (Ride Height)]=9" Squat.

Calculate the Proper Overall Spring Rate With the effective corner weight and required squat numbers known, all you need to do to find your required overall spring rate is to divide the weight by the squat distance.

Example:

1,000 lb. Load with 9" Squat needed.

[1,000 lbs. (Effective Corner Weight)] / [9" (Squat Needed)]= 111.11 Lbs./in. ~110 Lbs./in

Step 3: Choose Your New Spring Rates

Single Rate Coilovers (6" to 10" Coilovers) For single spring coilovers your calculation is done. Based on the example above, you would want to find a spring rate close to 110 lbs/in. which will likely be a 100 lb. spring.

Dual Rate Coilovers (8" to 16" Coilovers) Dual rate coilovers use two springs, so you will double the required spring rate and split the difference. Using the example above, 110 lbs/in. multiplied by two is 220 lbs./in. so you will want to find two springs that split that rate, in this case a 200 lb. upper spring and a 250 lb. lower spring.

Spring Rate (lbs./in.) = Load (lbs) / Deflection (in.)

*The lighter rate spring always goes on top. For spring rates up to 250 lbs. it is good to keep the separation at 50 lbs. Spring rates above 250 lbs. can have a 100 lb. separation between the springs. Using the same spring top and bottom works fine, however, you lose the ability to transition between different spring rates.*

Step 4: Choosing Spring Size

Coil Spring Diameter (Inner Diameter) Coilover shocks come in 2.0", 2.5", and 3.0" sizes and these measurement are based on the outside diameter of the cylinder. Springs, on the other hand, are sized based on their inner diameter and a very common mistake is to match the coilover size to the spring size. Coilover springs must actually be a bit bigger than the coilover to account for the ID shrinking as the coil spring compresses and twists. The proper spring sizes for each coilover size are listed below:

• 2.0" Coilovers use 2.5" ID Coil Springs

• 2.5" Coilovers use 3.0" ID Coil Springs

• 3.0" Coilovers use 3.75" ID Springs

Coil Spring Heights (Free Length) If your coilover has a raised bottom spring plate, then it is best to run two springs that match the travel of your coilover. If you have a 14" coilover with a raised bottom spring plate, then you would run two 14" tall springs. This is the preferred combination because it allows you to run each spring on the top or the bottom for simplified spring changes. For coilovers with flat bottom spring plates, the lower spring needs to be 2" longer than the travel of the shocks and the upper spring would match the travel. For example, a 14" coilover with a flat bottom spring plate would use a 16" lower spring and a 14" upper spring.

There are, of course, many exceptions to the above rule-of-thumb, including triple rate coilovers, cases where built-in preload is needed, and tight applications were coil-binding might be an issue. When in doubt, add up your coil spring heights including 3/4" for each slider and then subtract the squat and overall shock stoke and compare that with your spring compressed lengths and make sure everything works out with room to spare.

Interim Summary: We've covered a lot of ground to this point, so let's do a brief summary

• Suspension provides ride and handling - it's chief jobs are to prevent the wheels from loosing contact with the ground over rough terrain and to isolate occupants from that rough terrain.

• Springs support the weight of the vehicle and absorb the road shock of bumps and holes by compressing and rebounding.

• Shocks damp the oscillation of the springs by pumping a piston through a column of hydraulic oil.

• Revalveable- The amount of damping a shock provides depends on its valving.

• Springs and shocks combine to determine whether a suspension is firm or soft.

• Spring and shock selection is a careful compromise between ride and handling.

• Coilovers are an ingenious way to package shocks and springs as one convenient assembly, compact, easy to fit, frees room for link geometry and steering.

• Coilovers are long-travel, high quality, revalveable, gas-charged, mono-tube shocks.

• Coilovers use two or more coil springs in dual- or triple-rate setups, allowing a soft initial spring rate followed by a firmer spring rate as the suspension compresses.

• Completely rebuildable - parts are available separately at very reasonable cost.

• Tuneability - with a vast array of spring lengths and spring rates available, coilovers allow you to select spring rate for a specific target suspension frequency, and then use spring length and the built in adjuster to achieve a target ride height / suspension height.

• Multiple spring rate - easy to set up for use with a combination of springs, providing a soft initial spring rate that transitions to a firmer spring rate as the suspension compresses.

• Adjustability - built in adjustable top spring seat provides ability to adjust ride height, suspension height, & preload as well as accommodate different length springs with different amounts of spring travel. Adjustable stop ring provides ability to adjust position where spring rate transition occurs.