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Old 06-05-2015, 07:53 PM
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Extended/Collapsed Shock Length in relation to Coils/lift kits

I'm not 100% up to par on the mechanics of suspension. But I'd like to think I'm pretty mechanical savvy. With that said, I'd like to understand what I should be looking for in a shock to work with an aftermarket coil.

Some background: 2015 JKUR. Totally stock. Considering Rock Krawler's 3.5" X-Factor Lift. Stock MT's for the time being (if it matter's regarding question.) Shocks I've been drooling over are Fox's 2.5 Factory Series Reservoirs with Dual Speed Compression for the JK. (extends 26", collapses 15.9").

I'm not going to lie that the hardware is definitely going to be overkill for what my rig will probably encounter in its lifetime, but I don't want to turn this into a debate of why not buy for realistic use. I'll admit I'm going for some [email protected]#$ factor here too.

But in terms of specs on shocks: What do I need to know about the shock in relation to the coils (or lift kit). Will certain extended/collapsed shock lengths NOT work with certain lift kit coils? Is there a particular length range I should be looking for?

Lastly, what do I need to know about bump stops in relation to the above? I'm assuming stock bump stops are not the way to go?

Thank you in advance for helping me understand.

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Old 06-05-2015, 08:10 PM   #2
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Rock krawler recommends 17-29" for front and 17-27" in the rear, both with 3" bumpstops.

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Old 06-05-2015, 09:38 PM   #3
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26" of extend length is not much. The Rancho RS9000XL I just installed on my wife's JK have 26.8". On our JKU I run the 5100 Bilstein with my RK 2.5"(3.25" real world), these have a 27.5" extend length. A .8" to 1.5" might not sound like a lot but on the types of trails found here in SoCal or the SouthWest in general it can make a big difference. But all this is academic if along with your 3.5" lift you do not also install a new front drive shaft. The factory drive shaft will max out right around the 26" extended drop point of your shocks. This is not a good thing.


Here is an example of what can be achieved with shock length only. This is my wife's JK with only a TF 2.5" Performance budget boost and 9000XL shocks. At the point shown the shocks and drive shaft have about maxed out -1" left.
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Old 06-05-2015, 10:46 PM   #4
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Quote:
Originally Posted by 70R-1 View Post
I'm not 100% up to par on the mechanics of suspension. But I'd like to think I'm pretty mechanical savvy. With that said, I'd like to understand what I should be looking for in a shock to work with an aftermarket coil.

Some background: 2015 JKUR. Totally stock. Considering Rock Krawler's 3.5" X-Factor Lift. Stock MT's for the time being (if it matter's regarding question.) Shocks I've been drooling over are Fox's 2.5 Factory Series Reservoirs with Dual Speed Compression for the JK. (extends 26", collapses 15.9").

I'm not going to lie that the hardware is definitely going to be overkill for what my rig will probably encounter in its lifetime, but I don't want to turn this into a debate of why not buy for realistic use. I'll admit I'm going for some [email protected]#$ factor here too.

But in terms of specs on shocks: What do I need to know about the shock in relation to the coils (or lift kit). Will certain extended/collapsed shock lengths NOT work with certain lift kit coils? Is there a particular length range I should be looking for?

Lastly, what do I need to know about bump stops in relation to the above? I'm assuming stock bump stops are not the way to go?

Thank you in advance for helping me understand.
I just re-read your post and I must have glanced right over that you are going to run a RK 3.5" lift with "stock MT" tires. Is that correct? You are aware that the RK lifts run about an inch taller than advertised. So more like 4+ inches. I for what it is worth would urge you to forgo the reservoir shocks and instead run a less experience pair, put money first into proper sized tires for that lift hight. You can always replace the shock late. Bad ass shocks and looks aside stock MTs on a 4ish inch lift is questionable safety wise. Sorry if I over step myself just don't want to see a fellow SoCal Jeeper get hurt.
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Old 06-05-2015, 11:07 PM
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So here's a good spec chart I found on these shocks. I'm understanding the concept of utilizing the most travel you can get out of a shock with a particular lift kit. Thanks for the info. The shocks come in two ranges for specific lift heights. I guess this brings up another question.
If I were to go with the larger/longer shocks geared for the 4-6" lift to acquire additional travel, will this pose a problem?... The bump stop will keep the shock safe from becoming fully compressed (I think, correct me if I'm wrong)? Is it it problematic for shocks to have additional travel that isn't utilized?
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Old 06-05-2015, 11:13 PM
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Oh, and yes the plan would be to replace front and rear driveshafts....

The stock MT tires would be temporary. I'm planning on bumping up to 35's. But I hear what you're saying, I appreciate the words of caution, no need to apologize. It's a great idea......

Still, the info on the shocks is helpful. Thank you!
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Old 06-05-2015, 11:33 PM   #7
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I dont see how staying with a smaller tire is unsafe? It will look silly with that lift but...engine performance will be the same, braking, same. Center of gravity will be lower/better than with larger tires...
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Old 06-05-2015, 11:51 PM   #8
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I would go with the longer shock in the 4"-6" range. It's kind of " a better to have it and not need than need it and not have it " thing.

Setting the bump stops on the axles will be important to maximize travel and prevent damage to the shock. It does not hurt the shock to have up travel left. The same is true for down travel. Your suspension with new drive shafts has the potential to max out the down travel of the shock. If it does (that is A LOT of flex by the way) I would recommend the use of limiting straps. You do not want the weight of the axle supported by the shock and shock mounts. If you are having a shop install the lift make sure they have a test ramp. Good shops will ramp your Jeep and take measurement to help ensure proper settings of the bump stops and if straps are needed. If at all possible be there when they ramp it and take photos for you records.

Depending on where you live in SoCal there are a fair number of good and not so good shops. Here in the IE I like JPI based in Yuciapa. Not cheap, but none are. They have excellent customer service and are friendly folks.
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Old 06-06-2015, 12:34 AM   #9
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I dont see how staying with a smaller tire is unsafe? It will look silly with that lift but...engine performance will be the same, braking, same. Center of gravity will be lower/better than with larger tires...
First off I did not say "unsafe". I said "questionable safety". This indicates there may be factors that could lead to an unsafe situation. If you can not see the possible situations that can occur there is no way I can explain them to you.

Well maybe simple physics, taller the ladder the wider the base is for stability.
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Old 06-07-2015, 09:22 AM   #10
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Center of gravity will be lower/better than with larger tires...
Not necessarily. The height of the vehicle is increased by the weighted radius of the tire. But the increased mass of the tire is below the existing cg. Depending on the numbers, this may actually lower cg.
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Old 06-08-2015, 04:55 PM
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Thanks for the responses. I'll figure out what I'm going to do about the tires.
BBORTKO's post was correct on RK's recommendation for Extended/Collapsed shock lengths. RK lists 17-29 front and 17-27 rear with 2" bump stops. Since the shocks I'd like to get have a collapsed length of 17.3 front and 17.8 rear, does that pose any other type(s) of issue(s)?

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