Off-Road Shock Measurement Guide

Performance shocks, coilovers, and bypasses have much larger internal components than generic shocks so they take up more room for the same amount of shaft travel. This means you have less margin to work with and your measurements need to be spot on. This guide will show you how to measure for new shocks, coilovers, and bypasses.

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New Shock Measuring

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King Shocks

Step 1: Measure Your Compressed Lengths

**All measurements should be performed with the springs removed and the vehicle safely supported. If you do not have the proper equipment to do this safely, bring the vehicle to a professional.**

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.

Measuring for Shocks Measuring for Shocks Measuring for Shocks

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.

Measuring for Shocks

Step 2: Measure Your Extended Lengths

With the chassis of the vehicle safely supported, let the suspension hang down as far as it will go (full droop). Note that your limiting factor could be your drive shaft angle, CV shaft angle, your suspension system binding, or the extended length of your shocks.

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 truck might be better suited for more down-travel (larger shock).

Finally, you never want to bottom out on your shocks (except for ORI Struts) 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.

Compressed and Extended Lengths for Popular Shocks, Coilovers, and Struts
Measurements are from center of top mounting bolt to center of lower mounting bolt.

Size King 2.0 King 2.5 Fox 2.0 Fox 2.5 ORI STX Strut

6" 13.0" - 19.0" 14.0" - 20.0"

8" 15.0" - 23.0" 16.0" - 24.0" 17.5" - 24.4" 15.2" - 23.2"

10" 17.1" - 27.1" 18.4" - 28.4" 16.1" - 26.1" 19.5" - 29.4" 17.2" - 27.2"

12" 19.6" - 31.6" 20.7" - 32.7" 19.1" - 31.1" 21.5" - 33.4" 19.2" - 31.2"

14" 21.6" - 35.6" 23.3" - 37.3" 21.1" - 35.1" 24.5" - 38.4" 21.2" - 35.2"

16" 23.6" - 39.5" 26.0" - 42.0" 24.1" - 40.1" 26.5" - 42.4" 23.2" - 39.2"

18" 28.0" - 46.0" 26.1" - 44.1" 25.2" - 43.2"

Some shock manufacturers offer options that can change the compressed and extended lengths of a shock including extended lower rod ends, welded lower rod ends, different length shock shafts, shorter internal spacers, over the top cylinder caps, as well as various other options. If you have any doubts as to which shock size to go with, contact your favorite performance shock dealer.

King Shocks

Never Order New Shocks Based On Your Current Shock Lengths

King vs Generic Shock Size

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.

Vehicle ExampleVehicle Use Recommended Shocks

Mild Jeep on 35-37" Tires Street 2.0 Emulsion Shocks
Mild Jeep on 35-37" Tires Mild Offroad 2.0 Shocks with Reservoirs + 2.0 Hydraulic Bump Stops
Mild Jeep on 35-37" Tires Expedition 2.5 Shocks with Reservoirs + 2.0 Hydraulic Bump Stops

Buggy on 1 Ton Axles and 40-42" Tires Mild Trails 2.0 Coilovers with Reservoirs
Buggy on 1 Ton Axles and 40-42" Tires Rock Crawling 2.0 Coilovers with Reservoirs + 2.0 Hydraulic Bump Stops
Buggy on 1 Ton Axles and 40-42" Tires Rocks & Desert 2.5 Coilovers with Reservoirs + 2.0 Hydraulic Bump Stops
Buggy on 1 Ton Axles and 40-42" Tires Ultra4 Racing 2.0 Coilovers + 2.5 Bypasses + 2.0 Hydraulic Bump Stops

Full Size Truck with 40-44" Tires Mild Trails 2.5 Coilovers with Reservoirs
Full Size Truck with 40-44" Tires Hill-N-Hole 2.5 Coilovers with Reservoirs + 2.5 Hydraulic Bump Stops

Ultra Light Tube Buggy with A-Arms Recreational 2.0 Coilovers with Reservoirs
Ultra Light Tube Buggy with A-Arms Aggressive Use 2.5 Coilovers with Reservoirs + 2.0 Hydraulic Bump Stops

Desert Truck with A-Arms/Trailing Arms Recreational 2.5 Coilovers with Reservoirs + 2.5 Hydraulic Bump Stops
Desert Truck with A-Arms/Trailing Arms Mild Racing 2.5 Coilovers + 2.5 Bypasses + 2.5 Hydraulic Bump Stops
Desert Truck with A-Arms/Trailing Arms Hard Racing 2.5 Coilovers + 4.5 Bypasses + 2.5 Hydraulic Bump Stops

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, contact a reputable performance shock dealer like Filthy Motorsports and they will point you in the right direction.

Video: How To Measure For Coilovers

Other Coilover and Spring Resources

4-Link Suspension Guide
Coilover Installation and Setup Guide
Coilover Spring Re-Calculation Guide
Coilover Spring Rate Calculator
Performance Shock Tuning Guide
ORI STX Struts Guide Hydraulic Bump Stop Guide

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