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Old 05-18-2007, 06:18 AM   #1 (permalink)
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Coilover setup questions

In the process of rebuilding my front axle, I decided to go with coilovers up front to match the rear coilovers!

I'm getting 14in coilovers, just need to figure out what spring rates, and then figure out the mounting locations.

My question, is what spring rates are you guys running? Running the calculators I can find, I'm thinking 200/250 is what I will want.

I want to have it as close to done when the shocks get here (2 weeks out). But I want to make sure the mounts are built to the right height for my 6in lift (I'd like to stay around there). How can I figure out what the lenght of the coilover will be at ride height based on my spring rates and the weight of my XJ? I'm been running the numbers through the coilover calculator (/forum/general-4x4-discussion/215114-coilover-spring-rate-force-modeling-calculator-feedback-requested.html).

I think I'm slowly getting that calculator figured out:
Ride Height compression 4.995
Shaft travel remaining 9.005

SO If I'm reading that right, I will have about 5in up travel (stuffing the tires), and 9in down travel (droop)?

Those of you who are running 14in coilovers, what is the length of them at ride height, and what spring rates are you running??

Last edited by ralphXJ; 05-18-2007 at 06:28 AM.
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Old 05-18-2007, 08:08 AM   #2 (permalink)
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What are you figuring for a corner weight?

Just for reference, I have 12" coilovers, 175/300 springs which give a primary spring rate of 110 lb, 6" of shock shaft showing so also 6" of compression, which would mean a 660 lb corner weight. Mine is a buggy with no front bumper and the winch is in the pass compartment, so my front is going to be lighter than a full bodied XJ.

You might keep in mind that without coilovers, the good spring rates for XJ's are in the mid 200's. I'd go for the correct primary spring rate to get the ride height you want, with a secondary spring rate after 3-4 inches that will control your harder hits. This means a lower spring of at least 300 lb. I also would consider just making your mounts where they need to be to give you the up/down travel you want, then control the ride height with spring rate.........rather than first determining spring rate and then figuring your mounting locations. You can fine tune the ride height with the adjustment on the top of the c/o. I assume you're going to use tenders on that 14" c/o allowing a shorter spring, which will then allow you to have a stiffer primary rate to reach your desired ride height......which will handle better.

BTW, it would be easier to mount a 12", easier to get a good spring rate at ride height, and you likely won't be able to use all of the 14" travel anyway. Be careful to not bottom out your driveline u-joints with that much droop. (you do know that excessive droop allows for excessive unloading which hurts climbing ability and stability.......and if you use limit straps to control that then you don't need 14" shocks)
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Old 05-18-2007, 08:50 AM   #3 (permalink)
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I'm figuring around 650-700 for corner weight. Everything upfront is stock (bumper, engine stuff like that). Not running a winch, although might look into getting a small one to pull the front end down on hill climbs and stuff.

I'm looking at: 200lb - 12.00in spring and a 250lb - 16.00in spring which would give a primary spring rate of 111 lb.

The reason I'm trying to figure out ride height, or around there, is I wont be getting the coilovers for probably 2 more weeks, and I'd like to atlest get started building my upper mounts! Also I'd like to order the springs and stuff to come along with the shocks. I have a run in 4 weeks, so I will be cutting it close once they come in, I am hoping to get as much done as possible when they come in. i know they will need some fine tuning, but i can always do that after the event!

I'm looking for around 5in up travel, and 9in of down (not sure if i"ll use it all or not), and just trying to get an idea of where everything will be.
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Old 05-18-2007, 11:26 AM   #4 (permalink)
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I think you may be good with those rate. MY ZJ is fullbodied and practically similar in weight. I run 16" CO's and run 250/300 in the front and 150/300 in the rear. I think my top spring is to light in the rear.

Last edited by Tommy_M; 05-18-2007 at 11:26 AM.
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Old 05-18-2007, 02:44 PM   #5 (permalink)
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I think you may be good with those rate. MY ZJ is fullbodied and practically similar in weight. I run 16" CO's and run 250/300 in the front and 150/300 in the rear. I think my top spring is to light in the rear.
What length springs in the front? I think this is a good basis for my setup as i'm looking to run 16s with a suckdown winch. Is it a V8 or 4.0?
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Old 05-18-2007, 06:46 PM   #6 (permalink)
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I think you may be good with those rate. MY ZJ is fullbodied and practically similar in weight. I run 16" CO's and run 250/300 in the front and 150/300 in the rear. I think my top spring is to light in the rear.
There's a big difference 250/300 and 200/250. Plus, your 16's will need to compress more at ride height than what he wants for his 14's. I think what you're running, and what I'm running, shows that his 200/250 is probably too light.
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Old 05-18-2007, 09:40 PM   #7 (permalink)
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There's a big difference 250/300 and 200/250. Plus, your 16's will need to compress more at ride height than what he wants for his 14's. I think what you're running, and what I'm running, shows that his 200/250 is probably too light.
So what are you thinking would be closer for mine? 200/300? 250/300?
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Old 05-18-2007, 10:31 PM   #8 (permalink)
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Originally Posted by ralphXJ View Post
So what are you thinking would be closer for mine? 200/300? 250/300?

Well, based on what you've already said, you're figuring a corner weight of 650-700 lbs. If we split that and use 675, and you said you want 5" of compression at ride height, that comes out to a 135 lb primary rate. Using 250/300 would give a primary rate of 136 lb. If you went with a 200/300 combination, that's a 120 lb primary rate, and you could screw down the upper spring adjuster to get the exact ride height you want if needed.

Now, you're talking 5" compression at ride height, which means you'll have 5" of droop in the suspension travel and 9" of compression (not the other way around). Do you have the clearance for 9" of suspension uptravel with 5-6" of lift? That's a lot of uptravel, and you're tires could be into the fenders plus other clearance problems. Using the 111 lb rate you were talking about, and the 675 lb corner weight, that would give you 6" of compression at ride height, probably a little more reasonable assumption, but 8" of suspension uptravel is still quite a bit.

If you stuck with the 111 lb primary rate, I'd still go with a 300 lb bottom spring/secondary rate, which will give you much better suspension response once you're into the bottom spring on harder hits. The Currie/Deaver Jeepspeed coil is a 250/300 dual rate, so the initial 111 lb is light in comparison, so you'd want a good stiff secondary rate which you can then tune to how much travel to use before you're into it.

A few more thoughts..............
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Old 05-20-2007, 11:24 AM   #9 (permalink)
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What length springs in the front? I think this is a good basis for my setup as i'm looking to run 16s with a suckdown winch. Is it a V8 or 4.0?


I just went out and looked at the rig becuase I didn't want to give you misinformation. I had swapped out my 250 upper coils in the front to 200's. I run a 14" upper coil and an 18" lower coil both front and back. So my rates are 200/300 in the front and 150/300 in the rear. And like I said I think the rear upper spring is to light. And I think my rig still sits to tall. I would like to lower it another 3" at least. And it is a 5.2 V-8.

Sorry, for some reason i typed 250 in my earlier post........

Last edited by Tommy_M; 05-20-2007 at 11:27 AM.
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Old 05-20-2007, 12:50 PM   #10 (permalink)
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Well, based on what you've already said, you're figuring a corner weight of 650-700 lbs. If we split that and use 675, and you said you want 5" of compression at ride height, that comes out to a 135 lb primary rate. Using 250/300 would give a primary rate of 136 lb. If you went with a 200/300 combination, that's a 120 lb primary rate, and you could screw down the upper spring adjuster to get the exact ride height you want if needed.

Now, you're talking 5" compression at ride height, which means you'll have 5" of droop in the suspension travel and 9" of compression (not the other way around). Do you have the clearance for 9" of suspension uptravel with 5-6" of lift? That's a lot of uptravel, and you're tires could be into the fenders plus other clearance problems. Using the 111 lb rate you were talking about, and the 675 lb corner weight, that would give you 6" of compression at ride height, probably a little more reasonable assumption, but 8" of suspension uptravel is still quite a bit.

If you stuck with the 111 lb primary rate, I'd still go with a 300 lb bottom spring/secondary rate, which will give you much better suspension response once you're into the bottom spring on harder hits. The Currie/Deaver Jeepspeed coil is a 250/300 dual rate, so the initial 111 lb is light in comparison, so you'd want a good stiff secondary rate which you can then tune to how much travel to use before you're into it.

A few more thoughts..............

So if a 250/300 is closer to what I should be running, I'll run those numbers. Your saynig that I have my compression/extension numbers switched? I want it to have 5-6in uptravel at ride height, and 8-9 drop at right height. So basicly 5in of shaft showing. Am I thinking correctly there?

So does that mean that my: Ride Height compression 4.995 and Shaft travel remaining 9.005 is backward?
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Old 05-20-2007, 01:56 PM   #11 (permalink)
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So if a 250/300 is closer to what I should be running, I'll run those numbers. Your saynig that I have my compression/extension numbers switched? I want it to have 5-6in uptravel at ride height, and 8-9 drop at right height. So basicly 5in of shaft showing. Am I thinking correctly there?

So does that mean that my: Ride Height compression 4.995 and Shaft travel remaining 9.005 is backward?

Yeah, it's backwards. If you have 5" of shock shaft showing at ride height, then you have 5" of uptravel to use, and your shock is compressed 9" at ride height so you have 9" of droop to use.

If you want to compress your shock/springs 9" at ride height, that really changes your spring rate calcs. You'll need a much softer spring rate at ride height which could also give you lousy stability, and would mean you'd probably want to transition into your secondary rate sooner. If you really want that much droop you almost have to run a tender coil and a shorter upper spring so you have a prayer of getting a decent primary spring rate, and so you don't have spring force all the way to full extension whan the front end is light like when you're climbing or on a side hill. A tender coil makes it so you have no spring rate for the last 4-5" of droop, which means little when you're actually drooping, but means a lot when the front end is light and the springs are pushing you up.

Personally, I don't see how you can use 9" of droop without binding your driveshaft, nor do I see any advantage to have that much droop available. All I see with that much droop is a disadvantage. Many of us limit droop with a center limiting strap so we get better stability. On a decently set up rig with dual lockers, in most places stability will give you better performance than flex. Getting enough flex for good performance is so easy, it's a no brainer. Getting too much flex and loosing stability will decrease performance. As long as you're crawling through a fairly level rock garden or through big dips or washouts, a lot of flex is fine, but as soon as you have to climb, your rig won't work as well as someone with less flex and better stability. Now climb on something that is off camber or has big holes or dips and you won't even want to do it while the guy with great stability will go right up. I don't know what type of wheeling you do, so this is just general rambling. But, if all you want or have room for is 5" of compression, then the 7" of droop you would get with a 12" shock is plenty, especially in the front where you also have to create a steering system that can handle that much droop.

Hey, if you really want a 14" shock, I'll shut up.

Just keep in mind that you have multiple goals in building a suspension that performes really well.
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Old 05-20-2007, 02:23 PM   #12 (permalink)
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Thanks, that all really helps! Dont shut up, I'm getting a lot figured out!!

I'll have to look over the numbers again, might have to rething some of my mounting ideas, or switch to 12in coilovers. I can always add a limiting strap and keep things under control if I stick with the 14in coilovers.

I'm going to take some more measurments and see where my mounts would end up with 12 & 14in coilovers, see if I will need to cut the hood for either, and stuff!

Last edited by ralphXJ; 05-20-2007 at 02:27 PM. Reason: added a couple more things
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Old 05-21-2007, 02:05 PM   #13 (permalink)
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I think Goatman is right on here. I would shoot for 200# primary rate like what aftermarket coils use. 12" shocks will probably make your life a lot easier.

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Old 05-22-2007, 05:16 AM   #14 (permalink)
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So its sounding like 200/300 or 250/300 and a 12in coilover is probably what I should be looking at!?!

Other then too much travel, what are the problems with running 14in shocks? Just curious.

12in shocks for the rear as well?
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Old 05-22-2007, 07:43 AM   #15 (permalink)
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What kind of wheeling are you building to do, and what tire size? How much body?

Rear shock length is dictated by the space you have to mount them, unless you plan to cut the floor. Most of us run 10" shocks in the rear on full bodied rigs, and those have to be exactly the right length to not bottom out.
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Old 05-22-2007, 07:50 AM   #16 (permalink)
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I wheel in Ohio, so muddy trails and a few rocks, but get out to Paragon & Rausch Creek to play in the rocks a few times a year.

Running 35s right now, but plan on 37s very soon. Its a full body, the fenders are cut a lot for clearance, but compared to some, it still is basicly a stock body.

I'm currently running Rock Krawlers coilover conversion in the rear with some short coilovers (I think 8.5in) but I plan on cutting the floor and running longer ones up to the cage some time in the near future.
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Old 05-22-2007, 10:59 PM   #17 (permalink)
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I like the RK rear link/coilover setup, what about it doesn't work well enough for you?

Nothing wrong with improving and upgrading, just wondering what you're trying to improve.
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Old 05-23-2007, 04:40 AM   #18 (permalink)
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I love my RK kit!! The only complant I have is that since I'm only at 6in of lift (RK coilover kit is for a 8in lift) I had them send me shorter coilovers. The ride is amazing compared to leafs, however, the flex isn't any better then with my old leafs.

I'm just throwing around the idea of running longer coilovers in the rear to match the front. I'm not against cutting the floor, so I'm just thinking right now.
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Old 08-31-2007, 11:44 AM   #19 (permalink)
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Ok, I got the front done, and tested it out a bunch, its near perfect!!!! I went with 14in coilovers with 250/250 springs (125lb spring rate).

My rear coilovers are too stiff and have no travel!! They are the coilovers form my Rock Krawler coilover kit. They are 8.5in travel shocks, currently sitting with not much travel. They are running 225lb on the bottom with a compressed tender on the top. The valving is 35/45. So with a single spring, would I be safe to assume 225lb is my spring rate there?

I have a set of 12in ready to go on, just need to figure out my spring rates! Do I setup my rear coilovers to be the same, or lighter then the fronts? The rear's aren't terrible, but they are noticable now that the front rides so well!
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Old 08-31-2007, 12:38 PM   #20 (permalink)
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Got buildup thread? I'd like to see the mounting of your front coilovers.
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Old 08-31-2007, 01:10 PM   #21 (permalink)
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Nope, never got around to doing a build up thread. Its basicly what everyone has done! My welds suck, so I wouldn't want to post too many pictures anyway, I'd get flamed for sure!!

The front technicly isn't finished, I need to cap the ends of a few of the ends, and paint everything. Need to do some finish welding as well. Its done well enough, but need to touch up some stuff this winter.
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Old 09-02-2007, 11:25 AM   #22 (permalink)
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So the rear of the XJ, springs should be softer, or stiffer then the front?? I'm running a 125lb spring rate in the front, and currently have a 250 spring rate in the rear, which is too stiff.

Go closer to 150-175??
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