HOW TO: Measure for replacement Jeep Shocks
November 15, 2022
This article will help explain how to measure for new shocks on most Jeep Wranglers. Measuring for the correct length shocks will make sure you are getting the most performance out of your suspension. For the best ride quality possible, it’s important to have plenty of up and down travel. Continue reading below to learn more!
**Please read before continuing through this How To Article**
This article is intended for:
- Those maintaining OEM factory shock mounts top & bottom, front & rear. This excludes shock relocation mounts and bar pin eliminators.
- For someone who already has a lift kit with all necessary components and are looking to replace existing shocks for better performance.
- This article assumes you’re using the correct bump stop spacers with no tire clearance issues.
Measuring Shocks Note: Shock manufacturers sometimes have different methods of measuring shocks. See below on how to measure for Fox and King shocks with stem top mounts commonly found on the front of TJs, XJs, LJs, JKs.
Measuring for the compressed length of a shock is pretty simple, which we will discuss below. Measuring for extended lengths can be a little difficult since you will need to inspect for things that will start binding like: driveshaft, sway bar, brake lines etc…It’s also important not to let the coil springs come unseated (negative preload) at full droop. Too long of a shock with short arm suspension can also create some serious binding issues. Longer extended length shocks are NOT always the best idea, although very tempting.
Note: Some suspension & spring companies request specific shock compressed & extended lengths. This can certainly help, but can also limit your options unless you measure for yourself. There also may be other requirements that go along with those shock recommendations.
How to measure for replacement shocks
*If you have a stem top mount, please refer to the above diagram.
- Jeep needs to be on flat level ground, with normal weight added, standard ride height [reference diagram to the left]
- Measure center of shock bolt to center of shock bolt (A)
- Measure how much chrome shaft is showing (B) (Ignore the bumper, measure total chrome outside of the shock)
- Measure space between bump stop cup and bump pad on axle (C) Existing suspension setup:
- Shock length at ride height (A)
- Shaft showing at ride height (B)
- A-B = compressed length of that shock
- (C) actual up travel available, should be ½” to 1” shorter than B lengths
If shaft showing at ride height (B) is less than up travel (C) you either need longer bump stops spacers or a shorter shock. Flex out the suspension to test for tire clearance and figure out if a shorter shock will work.
Translate shock measurements into helpful info:
Both B & C measurements are telling you what your current up travel is. This is how far your axle is able to compress towards the frame when hitting a bump. These two measurements should be very similar, but C should always be slightly shorter. It’s very important to have the bump stops hit before the shocks bottom out. Note that on articulation it is normal for the shock to become the bump stop. The bump stop just needs to contact first on hard vertical hits.
Ideal up travel for a street driven, weekend warrior Jeep is 4-5”. Anything less you will be compromising ride quality at speed. More than 5” of up travel is good for more aggressive driving and off-roading. If you don’t have enough up travel you may need to flex out the suspension and check for clearance issues if you were to run a shorter shock.
With the proper amount of up travel, your Jeep will soak up bumps much better and allow for a smoother ride on and off-road.
Without enough up travel, the shock doesn’t have enough room to work and will bottom out frequently off-road. This will result in a rough ride that is not fixable without adding more up travel.
Why is up travel important?
When seeking a lot of flex off-road many people overvalue droop and undervalue up travel. This is partly because it is easier to get droop than uptravel, and also because it works well for dedicated rockcrawlers. Most Jeeps are not dedicated rockrawlers and would benefit greatly from more up travel.
Up travel allows the suspension to soak up bumps off-road. Competition crawlers drive at very slow speeds, while Jeeps generally drive much faster on the trail. Having more up travel will allow your suspension to soak up the nuisance rocks and provide a much more enjoyable ride.
Up travel allows for more balanced flex. When you have very little up travel the tire bottoms out quickly when articulating and starts to lift the chassis, which increases your center of gravity. With more up travel your suspension will articulate more evenly and the center of gravity will be more stable.
How much total travel should I have?
Now that we have discussed the importance of up travel, we need to discuss how it impacts total travel. There is no perfect number that will be correct. Total travel depends on your vehicle, lift height and which shocks you choose. In general you want at least 4” of droop from ride height. For vehicles with less than 8” of total travel the up/down travel should be split 50/50. Once you have more than 4” of up travel it is nice to gain more droop than up travel, example: 5” up, 6” down.
Picking out shocks
Ok so you have lengths of shocks you can use, now what? How and what shocks should you pick? Deciding on which shocks to get will depend on your budget and performance needs. We have an article that goes over 2.0, 2.5, 3.0 shocks that may help you decide between the different sizes.
Note: Specific lift height labeled shocks (example: 2-3.5” Lift Shocks) can be helpful but also misleading they are not always labeled correctly. Lift height will vary depending on trim model (ex: Sport, Rubicon, etc), spring manufacturer and additional weight from accessories added.
Based on your current setup and measurements taken, you should be able to find a close with similar measurements. If not, you can always look into adding lift spacers or swap to a taller spring entirely. Just keep in mind what your goals are and what parts are available to achieve them.
Once you have shock length measurements, you can usually narrow down something that is very close to what you need. Most Fox shocks on our website will list the shock lengths in the “Specifications” tab. If measurements are not there, you can always reference https://www.ridefox.com/. Some of the King shock lengths are listed on our site, but not all lengths are available at this time. Just remember Fox & King have different methods of measuring compressed and extended lengths.
Pro tip: If you really want to squeeze numbers and get the best travel numbers possible, we would suggest removing the springs to cycle the suspension fully. This will provide you with more precise numbers. This may allow you to do minor trimming to achieve a lot more up-travel.