This article will help guide you on how to measure for universal fit coilover shocks for a solid axle vehicle.

Over the years, high performance coilover shocks have become popular for off-road vehicles with custom built suspension. Going with a coilover shock can be a great option since they can be tuned and setup for just about anything. AccuTune Offroad specializes in tuning coilover shocks for anything from recreational 4x4s to extreme off-road racing. As a shock expert, we are determined to help customers pick the best coilover shock for their application, and do it right the first time. Below, we will go over a few of the essential measurements needed to choose the correct size coilover shock for your build and make a few recommendations along the way. 

Terminology:
Ride Height: The final height of vehicle sitting on level ground.
Full Bump: Axle is level, and compressed all the way up to the frame, with bump stops fully compressed.
Full Droop: Axle is furthest from frame until other components start to bind or rub.
Up Travel: From ride height, the amount of shock travel going to full compression.
Down Travel: From ride height, the amount of shock shaft travel you have going to full extension.

 

Fitment
When measuring for shock length, keep in mind the space and location of where these shocks will be mounted. Find a good place on the axle or control arm to mount the coilover shock. Try to mount the coilover shock as far out on the axle as possible. This will help with clearance issues that come into play during articulation. Keep enough diameter space to fit a 3.5″ or 4.0″ (Outside Diameter) spring on the shock for 2.0 & 2.5″ shocks, respectively. Also note any upper shock mount restrictions, like the hood or fenders.

Ride Height
With your build platform and off-road driving style in mind, you need to figure out what your approximate ride height will be. The lower you are the more stable the vehicle will be, however you may lose the ground clearance or up travel needed for high speed off-road driving. Ride height is more of a personal preference, there is no right or wrong height. Once the vehicle is at your desired ride height, you may want to bolt the tires onto the axles to check for ground clearance and fender clearance. Before cycling the axle for shocks, it would be ideal to have suspension links in place, or at least mocked up.

At this point, don’t be too concerned about ride height, as this may change once we start to narrow down shock length options.

Up Travel
With chassis sitting at ride height, jack the axle straight up as far as it will go until it hits the frame/engine or you encounter binding on driveshafts or steering. It would be a good idea to have the correct size tires you will be using mounted to the axle to check for fender clearance. Depending on the type of build (Rock Crawler Buggy, Prerunner etc.) take note of what hits or binds. If you are able to cut or re adjust something to get more up travel, this may be something to consider later on. At full bump, measure from where you will be mounting the bottom of the shock on the axle, to where you will mount the top of the shock. Now add 1″ to the overall length of that measurement. This extra 1″ will make up for the 5/8″ bumper stop on the shock shaft, and the 3/8″ of extra shaft showing. At full compression, we want to have a little extra room for movement, so the 1″ rule allows for that.

This will be your compressed shock length dimensions.

Minimum Up travel suggestions (solid axle)
Rock Crawling = 4”   Trail Riding = 5”   Desert Racing / Ultra4 Type = 7”
We suggest dedicating 1/3 to 2/3 of shock travel for up travel, depending on application.

Down Travel
Using the same concept for compressed shock length, we need to measure for the extended length of the shock. With the chassis still at ride height, lower the axle as far as you can until steering, driveshaft or something else stops you from going further. Do not go over board on drooping the axle. If you’re reading this, you’re probably not building a Trophy Truck so too much droop will cause issues. With your extended length measurements, you should start to have a good idea on what travel shock you want to run. Common sizes for off-road shocks are: 10″, 12″, 14″ and 16″.

Down Travel Suggestions:
9” droop max, otherwise springs too soft and the vehicle will not handle well.

Articulation
Once you have a pretty good idea where the axle will cycle up and down, it’s time to articulate the axle one side at a time. When the axle flexes, the shocks will get very close to the frame and tires. Keep an eye on these locations and check for clearance issues. Fenders, bumpers are also common areas where the tire will come into contact with. If you run into clearance issues, try repositioning the shock mounting location to alleviate rubbing or consider cutting fenders. Make sure to cycle both sides of the axles with tires spinning, turned both ways. During this phase of measuring, it’s important to be thorough and accurate. Note that the shock may bottom out on articulation, this is ok and helps to prevent the tire from getting into things.  Measure twice, order shocks once! Cycle axles/tires as much as you can to make sure everything is smooth. If you think you might go up a tire size later on, you may want to compensate for that now.

Summary Notes:
-1/3 to 2/3 of the shock should be up travel.
-Do not exceed 9″ of droop.
-14″ shocks are most common, then 12’s, then 16’s.
-It may be necessary to adjust ride height and repeat this process a few times.
-If you want more than 16″ of travel consider a Trailing Arm Suspension design.
-18″ coilovers offer very few spring choices.

 

Shock and Spring Consideration
Based on the measurements you have gathered, its time to check for shock options that are close to your specifications. Compare your compressed and extended lengths to the shocks you are considering, make sure you choose shocks with adequate up travel and down travel. If you find yourself wanting more shock travel, consider a trailing arm suspension setup (Coilover mounted to control arm).

Once you have an idea on the type of shock you want, we can take it from there. Simply fill out this quote request form with your vehicles information and email it into us. As part of our complimentary service, we will calculate springs rates and discuss tuning options with you. We will custom tune each coilover shock based on how the vehicles built and the way it will be driven, free of charge. Coilover springs also come with an unlimited spring swapping program, so we ensure you get the correct spring rates for your build.

If you have any further questions, please feel free to send us an email or call: Sales@Accutuneoffroad.com (424) 377-0808

Coilover Shock Quick Links:

Spring preload is an important, but often misunderstood concept and this article is going to clear things up.

 

 

How To Measure Preload:

Preload is a measurement of how much a spring is compressed at full extension of the shock.
Thread the upper spring adjuster down until it just touches the spring, you are now at 0″ of preload.
Every inch you thread it down from there is 1″ of preload. With a 1.0 Motion Ratio that also lifts the vehicle 1″. With a 0.5″ motion ratio that lifts the vehicle 2″.

If you want more lift and have the correct amount of preload then you’ll need stiffer springs.

If you want less lift then you need softer springs.

Preload & Spring Length:

Preload is independent of spring free length. An 18″ long, 100 lb/in spring with 1″ of preload will give you the same ride height as a 10″ long, 100 lb/in spring with 1″ of preload.

In both cases you’ve applied 100 lb of force before the vehicle weight collapses the spring. Because spring rates are the same each spring will collapse the same amount under the weight of the vehicle. The result is the same amount of ride height.

The only time spring length can affect preload is if there aren’t enough threads on the shock to get the desired preload, or if the springs will go to coil bind.

 

Why Do We Need Preload:

Everyone thinks about what happens when springs compress, but it’s also important to think about what happens when they extend. Spring preload pushes the tire down and makes the suspension work. On big bumps at speed the spring preload pushes the tires down to better follow the terrain and make a smoother, more controlled ride. Under articulation the spring preload increases tire contract pressure improving traction.

 

Why Do People Say: “Springs Just Hold The Vehicle Up”:

“Springs Just Hold The Vehicle Up” is a common saying stemming back to long travel off-road race trucks. For suspensions with 15+” of droop the springs are already very soft and changing preload has very little impact on spring force. A shorter travel vehicle with 6″ of droop will see a much larger change in spring force from an equivalent change in preload. As seen on the graph below, a long travel desert truck going from 0″ of preload to 3″ of preload only results in an 8% increase in spring force at 5″ of droop. While a more standard vehicle will see a 167% change in spring force for equivalent change in preload.

So as you can see accurate spring preload becomes much more important on shorter travel setups. The concept that “Springs Just Hold The Vehicle Up” has some merit on long travel setups but is not true for short travel and mid travel setups.

Can You Have Too Much Preload?

Springs work in both extension and compression so too much preload makes the springs too soft on compression. When this happens we have to compensate with shock valving and sometimes that can lead to harshness. We look at suspension as a complete package and every piece of it has a purpose and it all needs to work together. When you have too much preload the springs can’t do their part.

 

How Much Preload Should I Have?

For most applications 1″ of preload in the front, and 2″ of preload in the rear is a good starting point. If you’re purchasing springs from us we also check other factors to make sure you have the ideal spring rate. As a result we do break this guideline.

 

Some vehicle specific applications do have different preload requirements. For example Toyota Tacoma’s and 4Runners generally run 2″ of preload in the front. With the standard aftermarket 600 lb/in springs there is some adjustability in the Tacoma and 4Runner Coilovers.  But heavier Toyotas require installing 650 lb/in and 700 lb/in springs to achieve ride height. When installing the heavier springs the adjustability of the preload is substantially reduced. There is very little room on the body to reduce preload, and the springs go coil bind if you add too much preload. As a result it is important to choose the correct springs for the weight and lift height of your Tacoma or 4Runner. Luckily we can help you choose, and we offer free spring swapping if the rate isn’t correct.

 

Summary:

Spring preload is very important on shorter travel vehicles. Make sure you buy springs from a company that offers free and unlimited spring swapping (like AccuTune Off-Road 🙂 ). 1″ of preload in front and 2″ of preload in the rear is a good starting point, but some suspension systems require breaking the “rules”. Give us a call for all of your spring needs!

 

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Updated: 8/18/16

If you have determined your coilover springs are the wrong rates, this article will walk you through how to take the proper measurements in order for us to calculate the correct rates.

Spring rates and preload are not a one size fits all proposition, we adjust your rates for your ride and your terrain.

 

Initial Coilover & Spring Setup:

It is important to start with the correct setup or the measurements won’t be meaningful.

• Shocks charged to proper pressure
• Dual rate nuts not in use at ride height
• Bump stops not contacting at ride height
• Vehicle is at proper ride height

Contact us for calculating new spring rates if you aren’t able to achieve proper ride height with your current springs.

Three coilover spring scenarios:

Scenario 1: Springs are tight at full droop (Positive Preload)
Scenario 2: Springs are loose at full droop, without tender coils or triple rate springs (Negative Preload)
Scenario 3: Springs are loose at full droop, with tender coils that are always tight (Negative Preload With Helper Springs)

 

1: Positive Coilover Spring Preload:

With vehicle at ride height:

• Measure shock shaft showing (pretend like bottom out bumper doesn’t exist)
• Measure coilover threads showing above spring adjuster
• Record upper and lower spring rates

With vehicle at full droop:

• Measure shock shaft showing
• Loosen spring adjuster nut until springs start to rattle
• Measure coilover threads showing above spring adjuster

How much you moved the spring perch is how much positive preload you have.
Call us with the measurements and we will calculate new spring rates.

 

2: Negative Coilover Spring Preload (Loose Springs, No Tender Coil):

With vehicle at ride height:

• Measure shock shaft showing (pretend like bottom out bumper doesn’t exist)
• Measure coilover threads showing above spring adjuster
• Record upper and lower spring rates

With vehicle at full droop:

• Measure shock shaft showing
• Tighten spring adjuster nut until springs stop rattling
• Measure coilover threads showing above spring adjuster

How much you moved the spring perch is how much NEGATIVE preload you have.
Call us with the measurements and we will calculate new spring rates.

 

3: Negative Coilover Spring Preload (Loose Springs, WITH Tender Coil):

With vehicle at ride height:

• Measure shock shaft showing (pretend like bottom out bumper doesn’t exist)
• Measure height of tender coil
• Record upper and lower spring rates

With vehicle at full droop:

• Measure shock shaft showing
• Measure height of tender coil

The distance the tender coil expanded is how much NEGATIVE preload you have.
Call us with the measurements and we will calculate new spring rates.

 

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Updated: 8/18/16

Getting the correct coilover spring preload is the first step in setting up your suspension. So what is preload?  Preload is the initial (pre) tension (load) on your springs before carrying the weight of the vehicle.  Coilover spring preload is measured in inches, in other words, how many inches have you compressed the springs before applying weight.

Setting Initial Preload on New Springs or Coilovers:

Follow this procedure if you have just purchased new springs or shocks from us.

• Start with the springs and shocks installed on the vehicle.
  • Springs loose
  • Dual rate nuts high on the body, spring slider not touching dual rate nuts
• Screw the preload nut down while gently rattling the springs, when they stop rattling that is Zero Preload
• Measure and record how many inches of threads are showing above the preload nuts
• Every inch you screw the preload nut down is another inch of preload
  • Every inch you screw it up is one inch of negative preload
  • Screwing the preload nut down one inch will also increase the shaft showing by one inch
• Screw the preload nut down to give you the target preload
  • Contact us if you’re not sure how much preload you are supposed to have
• Adjust the preload up or down to give you the desired amount of shock shaft showing at ride height

 

If you have negative preload, or your preload is more than  +/-1″ from our target we should swap springs.

Read our article How To Calculate New Preload And Springs By Using Existing Springs in order to take measurements for the new springs.

 

 

 

 

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