Coilover Spring Rates

I just finished a search for coilover spring rates and got plenty of spring rate info, but all for conventional coils.

Im planning on picking up a set of 16" travel Sway-a-way 2.0" diameter coilovers with resevoirs and dual rate kits tomorrow and am still debating the spring rate I want to got with.

Seeing as how Ive decided to go with the dual rate kits, Im looking for suggestions on what spring rates are working best under the xj's out there that are currently running these.

I'd like the coilovers to be just soft enough for rock crawling, but just stiff enough to allow occasional street use, and some moderate jumping (It sees 3 to 4 feet of air). So a happy medium, if you will.

Ive calculated the following so far:
*wheel travel- about 24" from full stuff to full droop
*distance from longarm radius point to axle- 42"
*distance on said point coilover will mount- 42" (top of axle)
*angle that coilover will be laid back at- 6* (to help push axle forward)
*mounting distance inward from kingpin (toward the diff)- 9"
*weight of sprung front corner- 1000lbs
*weight of unsprung front corner - UNKNOWN!!!! Can somebody help me?

So far, as per Sway-a-way's web site, this nets me a main (heavy) spring with a rate of about 375 lb/in, and a tender (soft) of about 250 lb/in. Does this sound about right to you guys? Sounds a little soft to me.

Any advice or help from those of you who are in the know with this stuff would be extremely appreciated!!! TIA.

nobody? Dont wanna have to go to POR. :callme:

sounds way to stiff to me, I have 200/250 on my front, go to pirate and find the table Ed Stevens setup for them or see if you can get a response from him here

Thanks. I went to polyperformance.com and they dont even sell any 8" by 2.5" id coils for the dual rate kits that are that soft. They start at like 275 and go up to like 5 or 600. Anybody else got anything?

For a dual coil setup with a 16" travel shock you need 2 coils of 16" length. :wave:

Seriously? I would figure if you had two 8" coils, that would be 16" total of coil. With two 16's, I would think that even compressed, 32" of coil is a bit long, no?

Im not challenging in any way, since I am completely new to these things. I am just honestly curious cause the logic isnt adding up for me. :read: :dunno: :dunce:

I'm not even close to knowledgable about coilovers buy if I throw enough bad information out maybe someone will pipe up and correct me.

1. It's going to be tough to get springs that will survive 3-4 of air on a 4000 lb jeep and then be plush enough to work well in the rocks.

2. You have 16" of travel but you need enough spring to span the distance between the retainers. The spring on the shaft side has to be long enough to keep it from catching on the shock body when fully extended. I don't have measurments but I bet the minimum you would want to use on the shaft end of the shock is 16". The length of the second coil has a lot of factors. Ride height and the static length of the shock at your desired ride height will come into play. The adjusters affect spring rate as well as ride height if your adding more preload to the spring stack.

Did you get Ed's calculator working yet? I would suggest buying the springs last after spending a lot of time running through those. You have a lot of thinking and guessing to do.

ArcticXJ said:

I just finished a search for coilover spring rates and got plenty of spring rate info, but all for conventional coils.

Im planning on picking up a set of 16" travel Sway-a-way 2.0" diameter coilovers with resevoirs and dual rate kits tomorrow and am still debating the spring rate I want to got with.

Seeing as how Ive decided to go with the dual rate kits, Im looking for suggestions on what spring rates are working best under the xj's out there that are currently running these.

I'd like the coilovers to be just soft enough for rock crawling, but just stiff enough to allow occasional street use, and some moderate jumping (It sees 3 to 4 feet of air). So a happy medium, if you will.

Click to expand...

A 16" coilover has 16 inches of travel, and this requires a spring stack with at least 16-inches of space (open gap) between the coil turns. A coil in the rates we use are typically 40-60% space compared to length. A 16" long coil can have anywhere from ~6 to ~12 inches of travel before coil bind. To assure we have 16-inches of travel space in the coil stack we use 30-34 inches of coils (after careful selection).

The coils need to remain aligned on the shock body, even when the shock is fully extended with 16-inches of shaft showing. The alignment demands the lower coil (the coil over the open shaft) be at least 16-inches long so it can be held in allignment at both the end keeper and the shock body (where coil retainers and spacers can hold the coil in place on each end).

Spring rate is spring rate, regardless of the type of spring. Most tall lifted XJ's use a front coil rate between 200 and 250#/in. The factory rate is about 160#/in (maybe a little more for trailer tow packages). You need to decide if you want the primary or combined spring stack rate to be close to what seems to work well for most XJ's or something a little different (it's your choice, but it demands some thought)?

The lower the combined spring stack rate, the more likely you will be able to use the full travel potential of the long travel shock. The trade off is that the lower spring rate at ride height will tend to be tippy and allow the handling to be sloppy and unresponsive.

The quick fix to combat the sloppy handling is to block out the travel of the secondary spring near the ride height (use the secondary spring adjuster stop). This leaves the coil stack to work only the primary coil, after the secondary coil travel is blocked, usually (but not always) the primary coil is the stiffer coil in the coil stack.

This is one reason why we see a lot of 250#/in primary coils with XJ's and other vehicles with sprung corner weights around 750# and a coilover mount near the stock coil centerline, they default to a primary coil rate similar to the popular traditional XJ/ZJ/TJ lift coils when compressed deep into the shock travel.

The total combination of mount distance from the vehicle centerline, the distance from mount to the tire centerline, and the coilover mount angle do have effects on the resulting coil choice (the coil selection equations you found) but the resulting ride quality is not an exact science. The math was developed to get close for specific applications (they seldom tell us what they were), and the results are by no means qualified for all uses. The starting point for coil selection is likely to be just as wrong using the equations as using the experience from others choices.

Moving the shock mount closer to the kingpin usually allows for a lighter coil rate with the same transient handling (and a softer ride in a straight line), moving the shock mount closer to the pumpkin usually requires a stiffer coil rate to gain the same transient handling (with a harsher ride in a straight line). It's easier to simply locate the mounts where they will fit (and not conflict with steering and linkages) and then test fit a coil stack to check sprung weight. With the sprung force known on the coilover mount configuration the modeling and tuning can begin.

You may find you will need a triple coil spring stack to get the ride height and spring rate at ride height you want, with reasonable force resistance at full compression. This adds cost to the coil stack combination, but it also adds tuning capability. If you plan and budget to buy all the springs to do this up front, it results in a combination that can be changed easier (coil swap tuning) as you get used to the drive habits.

I hope this helps?

Ed Stevens:

My hats off to you. That is probably the single most helpful piece of knowledge offered to me ever on a web board. Cant thank you enough. :yelclap:
Ahhhhhhh, Okay....
Jeez im a fawking retard, LOL!!! (no offense to those of you with deficiencies)
I cant believe I didnt think of it that way. Duh. 16" travel equals one 16" spring for the length of the shock body, then another for the length of the shaft itself, at full extension!!! a 16" travel shock will be roughly 32" (+3 or so for the eyes) fully extended. I get it now.

Man, I cant believe I even had to ask, talk about feeling stupid.:anon:

Ed A. Stevens said:

A 16" coilover has 16 inches of travel, and this requires a spring stack .....blah, blah blah

Click to expand...

Ed did I ever tell you I hate you? Your clogging my browser up with too many bookmarks.

As always, :thumbup: