Coilover Shock & Spring Selection For Handling

 

There are two ways to get an off-road vehicle to handle well: sway bars or careful shock and spring selection.  This article is for those who want to optimize their handling without using sway bars.

 

Off-Road Handling is Mostly About Spring Rate

Without sway bars, the springs and valving must work together to prevent chassis roll.  While rebound and compression damping do impact chassis roll, spring rate is the primary driver of performance.  To get a better perspective it helps to imagine the chassis of a vehicle rolling a set distance at a set rate of speed.  Here is what happens during the corner:

  • Spring compresses on compression side
  • Spring extends on droop side
  • Rebound damping resists extension on droop side
  • Compression damping resists compression on compression side

Rebound damping is a function of spring rate, as spring rate increases so does the rebound damping.  So in the example above, three of the four things which impact roll resistance are related to spring rate.  Increasing spring rate is the easiest way to improve handling and results in the least performance degradation because rebound damping can easily be adjusted to match.

 

Design Your Springs to Use The Coilover Dual Rate Nuts

Designing your springs to use the coilover dual rate nuts is the first and most important step in improving handling performance.  As the vehicle rolls, the dual rate nuts will engage the lower spring only and increase the spring rate on the compression side of the vehicle.  Some care must be given to the lower spring selection to ensure it is capable of compressing enough and doesn’t go solid before the suspension bottoms out.  We recommend starting with 1″ between the spring slider and coilover dual rate nuts at ride height, but tuning is required because every vehicle and spring combination is different.  Be aware that putting the coilover dual rate nuts too close to the slider at ride height, or having too stiff of a lower spring can increase harshness.

 

Reduce Spring Preload

Reducing spring preload increases the spring rate and improves handling.  Preload is the measure of how many inches of spring tension coilovers have at full extension.  Having positive preload is necessary to make the axle droop properly over bumps and to provide traction when articulated.  In our article about choosing springs, we established that target preload is between 1/2″ and 6″.  For vehicles concerned with handling it is recommended to shoot for lower amounts of preload, in the example below, going from 2″ of preload to 1/2″ of preload resulted in a 19% increase in spring rate.  Be sure to measure preload with the coilovers and limit straps installed or you may end up with excess preload.

 

Choose Coilovers to Eliminate Excessive Droop Travel

Many vehicles run excessive down travel that hurts their handling performance, careful thought needs to be given to how much down travel is really necessary.  Spring rates decrease with droop travel because the springs need to be designed to have preload at full extension.  In the chart below you can see how reducing down travel 2″ resulted in a 28% increase in spring rate.   The amount of droop travel required for a good ride varies by vehicle, terrain and driver but excessive droop comes at the expense of handling.  Here are droop numbers for common applications:

  • Rock racer with 14″ travel = 5-6″ of droop
  • Sand rail with 24″ travel = 6″ droop
  • OEM Dodge Ram 2500 truck with 10″ travel = 4-5″ droop

 

The effects of preload and droop travel on spring rate:

Shock & Spring Selection For Handling

 

 

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How To Perform AccuTune Measurements

Motion Ratio

Measuring Motion Ratio is surprisingly simple, but take care, this is the most important measurement because it is used several times in out equations. Take measurements on both sides and average the result.

For Shocks Mounted To a Solid Axle:

  • Measure the angle the shock leans forwards or backwards
  • Measure the angle the shock leans in or out

For All Other Configurations:

  • For best results measure to the nearest 1/16”
  • Start with the vehicle at ride height
  • Droop the wheel ~4” below ride height (measured vertically), record the exact droop
  • Measure and record the distance between the shock mounts
  • Raise the wheel to ~4” above ride height (measured vertically), record the exact compression
  • Measure and record the distance between the shock mounts
  • The amount the shock moved between droop and bump divided by the amount you moved the wheel is your motion ratio

 

UnSprung Weight

Unsprung weight can be measured by removing shocks from the vehicle and weighing the axles, tires, wheel. If the weight can’t be directly measured with scales, we can look it up using our vast collection of data.

 

Sprung Weight

If the sprung weight can’t be directly measured with scales, try measuring the entire vehicle and subtracting unsprung weight.

For vehicles with existing coilovers and springs perform the measurements in this article.

For OEM vehicles we have had good success using published curb weights.

 

Total Wheel Travel

Measure shock shaft showing at full droop.

 

Up Travel

Measure shock shaft is showing at ride height.

 

Wheel Rate

For coilovers record upper and lower spring rate. (We will calculate these for you if you’re buying coilovers)

Many lift kit coil spring rates are available online, and we have a pretty complete selection as well.

Wheel Rate for leaf spring vehicles

  • Measure sprung weight.
  • Set the vehicle at ride height on a flat, level surface.
  • Perform the following measurements on both sides and take the average.
  • Measure vertical distance from leaf spring (at center pin) to chassis.
  • Droop suspension without anything limiting it (ideally done without wheels and tires or axles attached).
  • Measure the new vertical distance from leaf spring (at center pin) to chassis.
  • Wheel rate = (Sprung Weight) / (Droop)

 

 

 

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Performance Valving: Learn About AccuTune, ProTune and Other Valving Options

AccuTune

AccuTune is the most accurate way to get your shocks setup correctly.  Through decades of shock tuning and engineering we have created a set of equations that calculate the ideal shock valving for your ride.  We evaluate the suspension for harshness across small bumps, and control through the whoops.  Our calculations are backed by hundreds of data points across a wide range of vehicles.  Our AccuTune measurements page explains how simple it is to get the data. Find out what’s possible today.

 

ProTune

ProTune is the easiest way to get your shocks setup correctly without any vehicle specific data.  Provide us what data you do have, and we’ll match you up with another vehicle we have tuned.  We have a huge range of vehicles to choose from because of our huge assortment of shock dyno data: all brands and sizes of shocks are the same to us.

 

Pre-Documented Applications

We have a huge collection of pre-documented applications that make it easy to get high performing pre-tuned shocks.  Simply tell us what’s unique about your vehicle and we’ll customize them for you.

 

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The Difference Between Emulsion & Remote Reservoir Shocks

 

A brief review of shock design hierarchy needs to be included to paint a complete picture, emulsion monotube shocks are far superior to twin tube shocks in comfort, performance and durability due to their larger pistons, gas charge, and superior construction.

 

When people hear Remote Reservoir they immediately think heat dissipation, but that’s not the whole reason Remote Reservoir shocks are superior to Emulsion shocks.

 

One of the biggest advantages of remote reservoirs are the lower operating pressures due to a reduction in gas pressure build up. All shocks are a bit like an air shock where the piston rod displaces significant volume and causes a change in gas pressure. For an emulsion shock this can be a substantial change and some 2.0 emulsion shocks can build up to 600 psi.

 

The increasing and difficult to predict gas pressure causes problems:

  • Harder to select springs – pressure acts like a spring and lifts vehicle making it harder to calculate initial rates
  • Can cause harshness – progressive spring rate adds hard to predict force which could cause harshness (Fox standard compression valving is softer for emulsion shocks for a reason)
  • More harshness – high gas pressure causes MUCH more friction which causes harshness
  • Less durability – all that pressure is rough on seals which are now clamping on the piston rod with 3x the pressure

 

Emulsion vs Remote Reservoir Shocks

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How To Choose Coilover Spring Rates

Background on Coilover Springs

Spring selection is critical to the operation of your suspension.  Springs hold your vehicle up, provide cornering roll resistance, and make sure the suspension droops out properly. Below are some rules of thumb to help you select rates; unique applications may require breaking the rules (such as those with extreme amounts of down travel).

 

Rules of Thumb

Preload

Preload at the coilover should be between ½” and 6” to prevent the springs from coming loose and to ensure proper droop, wheel rate and bottoming control. Less preload gives you better handling and less sag when adding weight but reduces how well the wheel droops over bumps.  Common setups should use 1-2″ of preload in the front and 2-3″ in the rear.

 

When in doubt, shoot for more preload than less.  If your suspension isn’t drooping properly into a bump and you’re rebound is correct, try adding more preload with softer rates.

 

Coilover Dual Rate Nuts

In a dual rate coilover setup, the softer spring should not be less than 70% of the stiffer rate. Eg Do not exceed 70/100

 

Longer Lower Springs

Lower springs face two issues that can be resolved by selecting longer springs.  First is that on many shocks the springs aren’t long enough, and the body isn’t threaded far enough for the coilover spring slider to engage the dual rate nuts early enough in the travel.  When the coilover dual rate nuts are able to engage properly the lower spring collapses a lot more than the upper spring and the lower spring can go solid before the shocks are fully collapsed.  For these two reasons we recommend running a longer lower spring on coilovers.

 

Check out our Shock Tuning 101 article for more information on how to use dual rate nuts.

 

Coilovers ordered from us with springs & AccuTune valving receive a highly accurate spring rate calculation including 5 point performance check.

If you already have springs, and want to make adjustments to your rates, see our article How to calculate new preload and springs by using existing springs.

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Suspension Terms

  • Air Bump – A shock designed specifically for preventing bottoming out.
  • Air Shock – A shock which uses a large diameter shaft to act as a spring and damper.
  • Bleed – A hole through the piston through which oil can pass unrestricted.
  • Bypass – A shock which has external damping adjustment for predefined regions.
  • Coilover – A threaded body shock which has coilover springs installed on it.
  • Connecting members – things connecting sprung and unsprung weight such as A-Arms, suspension links and leaf springs.
  • Corner weight – the weight of one corner of the vehicle. Left and right sides may be slightly different.  For our calculators it is recommended to provide averages of left and right corner weights.
  • Dual Rate – A spring setup using two stacked springs, commonly with a cross over point when the upper spring stops collapsing and transitions fully to the lower spring rate.
  • Flutter stack – A type of shock valving where smaller diameter disks are inserted between larger diameter disks.
  • Motion Ratio – How much the shock moves in relation to how much the wheel moves. A motion ratio of 0.5 would mean the shock moves one inch for every two inches the wheel moves.
  • Preload – The amount of spring tension applied when the suspension is at full droop (limit straps installed). This is often measured in inches.  Preload is most commonly measured at the shock, but can also be measured at the wheel for comparisons between vehicles.
  • Pyramid stack – A type of shock valving where many disks are used, and each one gets progressively smaller or larger, and looks like a pyramid.
  • Smoothie – A smooth body shock.
  • Spring Rate – Upper and lower springs each have their own rate, when combined they form a new, softer rate defined by the following equations.
  • Sprung Weight – everything on top of the springs and shocks, includes roughly 2/3 the weight of connecting members.
  • Triple Rate – A dual rate setup with very short third upper spring which quickly goes solid. This setup is reserved for unique setups.
  • Unsprung Weight – weight of everything below the springs such as tires, wheels, solid axles, and roughly 1/3 the weight of connecting members.
  • Wheel Rate – This is the spring rate at the wheel, it takes into account the suspension motion ratio and is useful for comparing across vehicles.

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