Jk rear coilover experiments... - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 17 Old 01-15-2017, 07:57 AM Thread Starter
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Jk rear coilover experiments...

So I've been toying with some configuration ideas for a rear coilover on my 08 2 door.

A few things to point out. I would like to try to avoid mutilating the rear upper stock shock mounts beyond the point of being reusable. I'm not opposed to running mounts through the floor pan of the rear. But I would prefer to retain the option of using a backseat if at all possible. Lastly, yes I know and outboard setup would preform better. However; frenching the frame is not an option at all.

My intent is for this to be a reference thread for two door owners experimenting/or considering similar set ups.

Initial test set up:

Fox 2.0 12" non-resi coilover charged to 200psi. Springs: 12" 2.5/250 over 12" 2.5/100. 1" of preload on the top 100lb springs.

Rear bottom mount: Evo rock star skids sitting 1.5" higher than stock mounting point.

Rear upper: mounted in stock location using a synergy bar pin eliminator. Lowers stock mounting point by .5" (no, I have no intentions of driving this set up. Just looking for firm, tangible results from which to make further adjustments from).

This configuration netted 9" of lift. What does that ultimately mean? I had 3" of compression from the jeep sitting under its own weight. 8" of usable up travel but basically zero usable down travel.

Here's the visual results. Keep in mind, there is 2.5" of lift in the front.




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post #2 of 17 Old 01-15-2017, 07:58 AM Thread Starter
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post #3 of 17 Old 01-15-2017, 08:16 AM
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I would not even bother putting coil overs back there unless you just want to be one of the cool kids and would stick to a 10" travel to fit them back there. Conventional coils with a quality shock will give you good flex and ride.

You are running too much travel if you are using rock stars which give you ground clearance but force you to run more lift height for up travel with long travel shocks.

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post #4 of 17 Old 01-15-2017, 08:27 AM Thread Starter
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Jk rear coilover experiments...

Quote:
Originally Posted by thedirtman View Post
I would not even bother putting coil overs back there unless you just want to be one of the cool kids and would stick to a 10" travel to fit them back there. Conventional coils with a quality shock will give you good flex and ride.

.


I agree that there is no significant gains to be had from doing a rear coilover. Especially an inboard configuration. More so a case of having the parts laying around. Access to a 2 post lift. A few friends willing to help, and a healthy dose of curiosity. I'll likely end up going back to a more conventional set up. However if my experimenting, and that of others compiled in one location. Could benefit someone more intent on going that route. Well, info is a good tool to have in the box...


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post #5 of 17 Old 01-15-2017, 08:31 AM
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Why the 1" of preload on the shocks?
Are the coils going to drop out?
If not this is just creating an additional 1" of lift height.

Some build info here:
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post #6 of 17 Old 01-15-2017, 08:51 AM Thread Starter
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Quote:
Originally Posted by thedirtman View Post
Why the 1" of preload on the shocks?

Are the coils going to drop out?

If not this is just creating an additional 1" of lift height.


Nope. Again, just a starting point.


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post #7 of 17 Old 01-15-2017, 09:06 AM
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The starting point should be:
1. Measure how much room you have for shocks between your upper and lower mounts.
2. decide how much up travel/down you want.
3. Find the unsprung weight of the corners you are installing the coil overs on.
4. Determine what use the jeep is going to see.
5. How much lift do you want to run.

Once you have these things the rest is pretty simple. If you order your shocks from someone that knows what they are doing, they will determine the valving, the coil lengths and rates and the length of travel for the shocks.

It would have been more helpful if you would have included some measurements of what you have like the distances between the mounts and your corner weights. You could mount the same set up on a loaded JKU with a 40" tire hanging off the back and likely see about a 3" difference in ride height.

Some build info here:
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post #8 of 17 Old 01-15-2017, 10:07 AM Thread Starter
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Quote:
Originally Posted by thedirtman View Post
The starting point should be:
1. Measure how much room you have for shocks between your upper and lower mounts.
2. decide how much up travel/down you want.
3. Find the unsprung weight of the corners you are installing the coil overs on.
4. Determine what use the jeep is going to see.
5. How much lift do you want to run.

Once you have these things the rest is pretty simple. If you order your shocks from someone that knows what they are doing, they will determine the valving, the coil lengths and rates and the length of travel for the shocks.

It would have been more helpful if you would have included some measurements of what you have like the distances between the mounts and your corner weights. You could mount the same set up on a loaded JKU with a 40" tire hanging off the back and likely see about a 3" difference in ride height.


Again, I agree with all of this. I make it a point to read all of your threads regarding suspension. Had this been planned and I was ordering parts. I would have gone more along the guidelines as you laid them out as they make practical sense. However, I was simply using parts I had laying around or already installed. I knew which of the already installed parts I wanted to keep. I also knew how far I was willing to go on fabrication and modifying I was willing to go. For example; the stock upper shock mounts are not intended to bear the corner weight of a 2-door. So using that as a measurable mounting point isn't even an option. But by using that as a starting point. I know how much further up I would have to place an upper mounting point to get desired ride hight. And weather I was willing to make the sacrifices to achieve that. I also know how much compression I would get from the vehicles own weight given the coil set ups as they existed.

Overall was this the most direct route to get the desired result in the first try? Absolutely not. But since I had nothing invested but some free time. And the ultimate goal was just to see what happens if... Chances better than not, the coilovers will not remain on the jeep as I'm not willing to cut into the floor to make it work. But I learned some stuff and some friends and I had a good time messing around with the idea. Nothing invested. Nothing lost.


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post #9 of 17 Old 01-15-2017, 07:40 PM
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Quote:
Originally Posted by thedirtman View Post
Why the 1" of preload on the shocks?
Are the coils going to drop out?
If not this is just creating an additional 1" of lift height.
You should be running preload with coilovers. You want the lightest springs that will support the weight of the jeep and then preload them 2"-3" to dial in your ride height.

OP now that you have springs under it you can measure them and figure out your corner weight and get new springs that are correct based on your weight and desired height.
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post #10 of 17 Old 01-15-2017, 08:55 PM
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You don't need to run 2-3" of preload with coil overs. You only need preload to adjust height after you have got the preload ring set to zero. If you are running 3"+ you should have either a higher rate on the coil or a longer coil.

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Last edited by thedirtman; 01-28-2018 at 09:02 AM.
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post #11 of 17 Old 01-16-2017, 06:00 AM
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Quote:
Originally Posted by thedirtman View Post
You don't need to run 2-3" of preload with coil overs. You only need preload to adjust height after you have got the preload ring set to zero. If you are running 3" you should have either a higher rate on the coil or a longer coil.
Running preload for the sake of running preload has no benefit.
The preload helps push the axle down in the last few inches of travel to keep the tire in contact with the ground. Running heavy springs to hold the Jeep up is counter productive to shock tuning. Look at any rig that has spent time tuning their shock and you will find a decent amount of preload.
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post #12 of 17 Old 01-16-2017, 07:58 AM
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Originally Posted by spedly View Post
The preload helps push the axle down in the last few inches of travel to keep the tire in contact with the ground.
But that'll also lead to worse unloading. ORI's take the opposite approach and are typically set to pull the axle up during the last few inches of travel and only the weight of the axle pulling down actually gives you that travel.
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post #13 of 17 Old 01-16-2017, 12:43 PM
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lots of preload may be beneficial to high speed off road racers to help with rebound but lots of preload on a rock crawler or daily driver will mean a stiffer ride and reduce the ability for the suspension to compress under slow crawling. It depends on the build. Most of the JK's that are running coil overs are not racing Koth (they will be running bypass as well). Even so you have nearly a half ton of axles and wheel pulling the wheels down as well as a 150psi+- gas charge and then yes the coils. Preload may be something you have to do as far as tuning frequency of the front and rear suspension and may not be able to be avoided.

Running short coil with lots of preload can create more unloading, more side to side movement, (not body roll) and you may be fully collapsing the coils at full bump.

Not saying that running preload is bad and is fine if you want to run it as it is a part of tuning and some just don't want to take the time to swap coils but saying you should run 2"-3" on any coil over set up is not correct.

Some build info here:
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post #14 of 17 Old 01-16-2017, 02:00 PM
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Preload is important for pushing the axle down both in the whoops and in the rocks. How much preload you should have depends on what you're doing with the vehicle in question (racing vs DD).

ORI's work with extremely high spring rates and negative springs, when flexed they won't generate the traction that a properly setup coilover will.

Unloading can be spring related, but a vehicle with proper valving and suspension geometry won't have unloading issues.

All rear JK lift springs I'm aware of are too stiff or too short to work to their fullest potential off-road. Coilovers are a great solution.


Light springs, light rebound, heavy compression are how to make your Jeep kick ass off-road, but if you mess up any one of those things it could be worse than heavy springs, heavy rebound and light compression. The benefits are well worth the challenge though.

https://www.instagram.com/p/BO0YOsqB...ccutuneoffroad

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post #15 of 17 Old 01-16-2017, 02:15 PM
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Quote:
Originally Posted by thedirtman View Post
lots of preload may be beneficial to high speed off road racers to help with rebound but lots of preload on a rock crawler or daily driver will mean a stiffer ride and reduce the ability for the suspension to compress under slow crawling. It depends on the build. Most of the JK's that are running coil overs are not racing Koth (they will be running bypass as well). Even so you have nearly a half ton of axles and wheel pulling the wheels down as well as a 150psi+- gas charge and then yes the coils. Preload may be something you have to do as far as tuning frequency of the front and rear suspension and may not be able to be avoided.

Running short coil with lots of preload can create more unloading, more side to side movement, (not body roll) and you may be fully collapsing the coils at full bump.

Not saying that running preload is bad and is fine if you want to run it as it is a part of tuning and some just don't want to take the time to swap coils but saying you should run 2"-3" on any coil over set up is not correct.
It isn't about running short stiff springs. You need to run the right springs. I've got 16" 100lb over 18" 150lb springs on 16" coilovers on the back of my jk with 2" of preload. Those are far from short or stiff.
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post #16 of 17 Old 01-16-2017, 03:00 PM Thread Starter
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Quote:
Originally Posted by spedly View Post
It isn't about running short stiff springs. You need to run the right springs. I've got 16" 100lb over 18" 150lb springs on 16" coilovers on the back of my jk with 2" of preload. Those are far from short or stiff.


I did this test with 12"x100 over 12"x250. The 250 was obviously too stiff of a spring for a jk with no spare, no bumper, no seat, etc...


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post #17 of 17 Old 01-16-2017, 07:06 PM
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Quote:
Originally Posted by spedly View Post
It isn't about running short stiff springs. You need to run the right springs. I've got 16" 100lb over 18" 150lb springs on 16" coilovers on the back of my jk with 2" of preload. Those are far from short or stiff.
I agree, the coils need to be the correct rate. Two rigs that do different things may use different rates as well.

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