coilover spring rate issues

Vanimal · Apr 7, 2012

so i got some 16" coilovers for the rear of my xj along with a 3 link setup.
got everything fabbed up and found out that the coils are way too stiff, which is what i kind of expected. i got them brand new and had the company i got them from set them up for me. the rates were 200 and 300. my problem is that there's waayyyy too much shaft showing. like 3" too much. and trying to find 16" springs in lighter spring rates is harder than i expected, i dont see much under 200lbs except for some no name brands. anyone have some ideas where i should be at or where to get coils? i'm looking to get about 50-55% droop. the coilover is pretty much perpendicular to the axle, and it is mounted to the top of the axle as well.

Goatman · Apr 8, 2012

You currently have a 120 lb primary spring rate, which is stiff for the rear. Many run 200/300 in the front, which is heavier. Spring rate is calculated by multiplying the two spring rates together (200x300=60,000) and dividing that by the sum of the two spring rates (200+300=500), so the rate is 120. Now measure how many inches the coils have compressed at ride height, which would be total shock compression IF the upper coil seats against the top when the shock is fully extended. You probably have a 16" coil and a 14" coil, so a total length of 30", so measure the length of the two coils at ride height and subtract the width of the slider, and subtract that from 30", and you have spring compression at ride height. Multiply your spring compression by 120, the primary spring rate, and you have your corner weight. An example would be 6" of spring compression, times 120, so you have a corner weight of 720 lbs.

Now figure how much compression you want at ride height, let's call it 8". Divide 8 into your corner weight of 720, which is 90. So, you want a 90 lb primary spring rate to get the ride height you want with those shocks. Use the above calculation to come up with combinations that will give you a90 lb primary rate. For example, 150/300 or 200/200 would give you a 100 lb primary rate.

Now, you actually have a bit of a problem, since a 90 lb primary rate is most likely too soft and you won't like the handling. This is caused by having too long a shock and needing to compress the springs too much to get to your desired ride height. The solution is to use a triple rate kit, and a shorter spring. Instead of using a 14" and 16" long coil, use a 12" and a 16" coil, so now instead of having to compress the springs 8" you only have to compress the springs 6" to get your ride height. So, 720 divided by 6 is 120, so you need a 120 lb primary rate.......but with 2" shorter springs. The triple rate kit uses the no load top spring that only serves to keep a little tension on the coils at full extension so they don't rattle around, but it adds no overall spring rate and collapses completely with the weight on the springs.

Hope that helps.

Vanimal · Apr 8, 2012

thanks richard, that helps some, although i'll have to read it over a few times i'm sure.

the springs are both 16" though.

as for the tripple rate kit, i was looking at that and i was curious how traction is if you're low corner is at the very end of the stroke so that you dont have the normal springrate pushing down on that wheel, but only the keeper spring. with lockers i guess it doesnt matter a whole lot i assume, but just curious if it hurts. how about keeping the 200 and 300 but going with the keeper spring on the top? i have a ton of threads left for the lockrings, i can likely get enough turns in there to get it as low as i need. is this a bad idea?

Tacedaddy · Apr 8, 2012

I've delt with ground control before with my BMW racing stuff (they are Ebach springs) but they will do custom rates and lengths and their costumer support is top notch. You are going to have to call them because im sure they wont have "jeep" stuff

EricsXJ · Apr 8, 2012

Thanks for posting that Goatman. That will come in handy for me too. :yelclap:

rockclimber · Apr 8, 2012

Goatman said:
You currently have a 120 lb primary spring rate, which is stiff for the rear. Many run 200/300 in the front, which is heavier. Spring rate is calculated by multiplying the two spring rates together (200x300=60,000) and dividing that by the sum of the two spring rates (200+300=500), so the rate is 120. Now measure how many inches the coils have compressed at ride height, which would be total shock compression IF the upper coil seats against the top when the shock is fully extended. You probably have a 16" coil and a 14" coil, so a total length of 30", so measure the length of the two coils at ride height and subtract the width of the slider, and subtract that from 30", and you have spring compression at ride height. Multiply your spring compression by 120, the primary spring rate, and you have your corner weight. An example would be 6" of spring compression, times 120, so you have a corner weight of 720 lbs.

Now figure how much compression you want at ride height, let's call it 8". Divide 8 into your corner weight of 720, which is 90. So, you want a 90 lb primary spring rate to get the ride height you want with those shocks. Use the above calculation to come up with combinations that will give you a90 lb primary rate. For example, 150/300 or 200/200 would give you a 100 lb primary rate.

Now, you actually have a bit of a problem, since a 90 lb primary rate is most likely too soft and you won't like the handling. This is caused by having too long a shock and needing to compress the springs too much to get to your desired ride height. The solution is to use a triple rate kit, and a shorter spring. Instead of using a 14" and 16" long coil, use a 12" and a 16" coil, so now instead of having to compress the springs 8" you only have to compress the springs 6" to get your ride height. So, 720 divided by 6 is 120, so you need a 120 lb primary rate.......but with 2" shorter springs. The triple rate kit uses the no load top spring that only serves to keep a little tension on the coils at full extension so they don't rattle around, but it adds no overall spring rate and collapses completely with the weight on the springs.

Hope that helps.

*right click, Save*

:clap:

fantastic info.

Goatman · Apr 8, 2012

Vanimal said:
thanks richard, that helps some, although i'll have to read it over a few times i'm sure.

the springs are both 16" though.

as for the tripple rate kit, i was looking at that and i was curious how traction is if you're low corner is at the very end of the stroke so that you dont have the normal springrate pushing down on that wheel, but only the keeper spring. with lockers i guess it doesnt matter a whole lot i assume, but just curious if it hurts. how about keeping the 200 and 300 but going with the keeper spring on the top? i have a ton of threads left for the lockrings, i can likely get enough turns in there to get it as low as i need. is this a bad idea?

Well, if you have adjustment left at the top then you don't have a problem, just move the top collar up and lower the ride height. Traction isn't an issue, you have lockers. Keeping a tire on the ground with the weight of the tire and axle should be better than carrying a tire, but it doesn't matter, the other tires are doing the work. Flex doesn't matter, remember, flex doesn't matter. Did I say flex doesn't matter?

If you're concerned about not having weight on the tire, then go with a shorter shock, which is just fine since flex doesn't matter.

I think a 16" shock is pretty long for the rear of a full bodied XJ unless it's on a pre-runner. You want a spring rate that's going to give you some stability and won't flop on steep climbs. Have you ever seen a rock crawl vehicle not go through a rock garden? Flex or carrying a tires doesn't matter, they all go through the rock garden. Now, get to the off camber obstacle and the waterfall, and one rigs works better than the other.......when stability matters and flex has nothing to do with it.

rockclimber · Apr 8, 2012

we know flex doesn't matter... but what about fl3x?

Vanimal · Apr 8, 2012

Goatman said:
Well, if you have adjustment left at the top then you don't have a problem, just move the top collar up and lower the ride height. Traction isn't an issue, you have lockers. Keeping a tire on the ground with the weight of the tire and axle should be better than carrying a tire, but it doesn't matter, the other tires are doing the work. Flex doesn't matter, remember, flex doesn't matter. Did I say flex doesn't matter?

If you're concerned about not having weight on the tire, then go with a shorter shock, which is just fine since flex doesn't matter.

I think a 16" shock is pretty long for the rear of a full bodied XJ unless it's on a pre-runner. You want a spring rate that's going to give you some stability and won't flop on steep climbs. Have you ever seen a rock crawl vehicle not go through a rock garden? Flex or carrying a tires doesn't matter, they all go through the rock garden. Now, get to the off camber obstacle and the waterfall, and one rigs works better than the other.......when stability matters and flex has nothing to do with it.

the reason for the longer shocks was because it wasnt much more $ at all to go with them over 12-14", and i didnt think the extra travel would hurt i could always limit it if need be i guess. who knows where i'm going to take this thing down the road, i didnt want to turn it into buggy and end up having to buy another set of $1k shocks. another factor is being able to drag myself over stuff that i dont neccesarily have the ground clearance for. if my tires can drop down and make contact it may be enough to get me over certain things where i normally would be high centered.
i guess neither reasons make up for a lack of stability though. so i guess i will figure out my corner weight, and run some numbers using the formulas you gave to see what i come up with and report back. appreiciate the guidance, it's good to hear this info from someone who has been there-done that, especially since im pretty much a complete noob with a jeep that was pretty much stock 2 weeks ago. :gee:

Goatman · Apr 8, 2012

Vanimal said:
the reason for the longer shocks was because it wasnt much more $ at all to go with them over 12-14", and i didnt think the extra travel would hurt i could always limit it if need be i guess.

Understandable. I hear that all the time. In the end, though, the extra length can be a detriment, so the free/inexpensive travel that can't be used isn't worth what you paid for it. Plus, a longer travel shock has a longer body which makes packaging more difficult and can limit critical up travel, especially if the goal is a lower ride height with good travel.

Sounds like you're doing fine, and asking a lot of good questions.

Vanimal · Apr 8, 2012

Goatman said:
Understandable. I hear that all the time. In the end, though, the extra length can be a detriment, so the free/inexpensive travel that can't be used isn't worth what you paid for it. Plus, a longer travel shock has a longer body which makes packaging more difficult and can limit critical up travel, especially if the goal is a lower ride height with good travel.

Sounds like you're doing fine, and asking a lot of good questions.

thanks Richard.
the goal was to stick to about 3-4 inches of lift with just as much wheel travel as i would ever need. i wasnt planning on going with huge tires, maybe 33's max. here's my build thread if you havent seen it. this page shows the shock towers i made along with the suspension linkages and whatnot. if you go back a few pages you can see how it was made. http://www.naxja.org/forum/showthread.php?t=1079954&page=10

some issues i'm running into on this build is tire clearance when flexed out (i know, flex doesnt matter!). even my 31's rub before the shocks bottom out. i can work the rear qp's some to help, but i think it's going to be the case no matter what unless i bump stop. my total uptravel will be limited by the top of the axle truss hitting the crossmember where the stock shocks mount, followed by the lower control arms hitting the bottom of the frame rail.
i had thoughts of trimming out that crossmember where the shocks mount, which would give me about an inch more of uptravel, however i do not know how much structural integrity that gives the body, although it doesnt seem like much. i would venture to guess my rear bumper is sturdy enough to make up for that, and i can always plate the rear sheetmetal behind the bumper as well.
for the lower control arms, i was considering putting a slight bend in them so that they dont hit the frame before the axle hits the bumpstops, however i am not sure what that would do for my antisquat. any thoughts there? the control arm brackets are mounted on the bottom of the frame rail.
The rear suspension and axle setup is from that red ZJ that Eric had in the back of your shop, if that helps. it's pretty much set up the same way except i replaced some poly bushings that seemed to bind with some johnny joints.

so i think the packaging and uptravel issues caused by the shocks are taken care of. do you think that going with a triple rate spring setup and proper rate springs will cure any detrimental effects of having the longer shocks, or am i still looking at sub par handling/stability no matter what?

Goatman · Apr 8, 2012

If the length of your shocks isn't limiting up travel, then the shock length isn't a problem on it's own. You can just get a shorter upper spring and limit strap it where you want, to fine tune the spring rate and ride height, if needed. Putting a bend in the LCA won't effect link geometry, you only work with end to end, what's in the middle doesn't matter.

I wouldn't modify the stock crossmember that the stock shocks bolt to, unless you replaced it with something stronger. The floor has a tendency to buckle and crack in that area, so you don't want to weaken it further.

That's a pretty low lift height for that much travel. You're going to have to be willing to do some major cutting and reworking, which might not be worth the trouble, or just go with a little more lift. How much travel out of the front with that lift height? The front is more trouble than the back when you're looking for up travel.

Vanimal · Apr 8, 2012

Goatman said:
If the length of your shocks isn't limiting up travel, then the shock length isn't a problem on it's own. You can just get a shorter upper spring and limit strap it where you want, to fine tune the spring rate and ride height, if needed. Putting a bend in the LCA won't effect link geometry, you only work with end to end, what's in the middle doesn't matter.

I wouldn't modify the stock crossmember that the stock shocks bolt to, unless you replaced it with something stronger. The floor has a tendency to buckle and crack in that area, so you don't want to weaken it further.

That's a pretty low lift height for that much travel. You're going to have to be willing to do some major cutting and reworking, which might not be worth the trouble, or just go with a little more lift. How much travel out of the front with that lift height? The front is more trouble than the back when you're looking for up travel.

thanks, that makes me a feel a little better about the shock length.
as for cutting and reworking, are you talking about tire/axle to body/frame clearance, or housing the shocks so that they don't bottom out before the axle/tires do? the shock towers are already built, tons of room for the shocks. it's tire/axle clearance that's causing uptravel issues now.
As for the front, i was planing on running a shorter travel shock, maybe 12-14". it will be some work, but i think i can fit 14's in there. obviously i'll need to do a bit of work, but i think it's doable. for now, i'll be running regular springs until i can spend the coin on some more coilovers. it will suck, but the coilovers will come soon enough.
here's my rear coilover shock towers. the link i posted before shows the whole build.

Goatman · Apr 8, 2012

Is this a go fast desert car or a rock crawler? 12" shocks are plenty up front, either way, depending on how serious you are about going fast. With proper tuning, and willing to use the travel, longer is almost always better for going fast, but not if you can't use it. For trail work and crawling 12" up front is way good. But, if the goal is low and stable, you can get by easily with less shock length.

rockclimber · Apr 8, 2012

I'm running 12" short body 7100s up front, I mounted my shock mounts off the LCA mounts. if I kept to that series of shock, I have room to mount and fully use a 14" shock. thats with 4" lift, 33" tires, ~6" of up and ~8" of down. with the 12" shocks I have ~5" of up and ~7" of down using polyperformance shock adapters that space the eye ~2" down from the stock mounting point.

Goatman · Apr 8, 2012

rockclimber said:
I'm running 12" short body 7100s up front, I mounted my shock mounts off the LCA mounts. if I kept to that series of shock, I have room to mount and fully use a 14" shock. thats with 4" lift, 33" tires, ~6" of up and ~8" of down. with the 12" shocks I have ~5" of up and ~7" of down using polyperformance shock adapters that space the eye ~2" down from the stock mounting point.

And your spring unseats at the top at full droop, so while it might be worth something rockcrawling it's questionable that the extra droop after the spring unseats will add any go fast performance.

Since we're on the subject of shock length, and usable shock length, I might as well repeat something that comes up regularly when talking to people about what shock length to get. Myself, Paul S, Dave Taylor, and Farmer Matt all have had XJ based buggies for quite a while, and we all did some go fast stuff racing to and from the trail before king of the Hammers and Ultra4 racing came about. All of our buggies work pretty well and compare well on the trail to any buggy that we might wheel with. We all have 12" front shocks. In Ultra4 racing, the Jimmy's 4x4 chassis have done pretty well, with Loren Healy and Derek West winning and placing well in a good number of KOH and Ultra4 races. The Jimmy's buggies come (or at least came the last few years) with 12" front shocks. So, KOH has been won with 12" front shocks.

Now, I'm not saying that longer shocks aren't better, or that you can't make longer shocks work, but a 12" shock can be made to work VERY well. Also, matching the shock length to the rest of the suspension and tuning the spring rate and valving is much more important than just getting the longest shock that can be squeezed into the spot. The Jeepspeed XJ's are pretty fast compared to most pre-runner and recreational XJ's, and they are limited to 10" of front suspension travel.

Vanimal · Apr 8, 2012

i'd like to be able to do both, however i do know that it's hard to do that since they're completely different animals. but i would always lean towards crawling since that's more fun for me.

rockclimber · Apr 9, 2012

Goatman said:
And your spring unseats at the top at full droop, so while it might be worth something rockcrawling it's questionable that the extra droop after the spring unseats will add any go fast performance.

at full droop, the spring unseats about 2" thats why I'm looking to run a progressive spring. I'm leaning hard at the Currie's, Gerald/John's KOH EMC car was running them and gerald said the spring stayed seated for the entire stroke of their 14" kings.

Now, I'm not saying that longer shocks aren't better, or that you can't make longer shocks work, but a 12" shock can be made to work VERY well. Also, matching the shock length to the rest of the suspension and tuning the spring rate and valving is much more important than just getting the longest shock that can be squeezed into the spot. The Jeepspeed XJ's are pretty fast compared to most pre-runner and recreational XJ's, and they are limited to 10" of front suspension travel.

its why I went with the 12"s... I saw no reason to go to anything greater, especially with stock suspension geometry. I can't really use more than 7" of droop, and the only reason I went greater than 10" is to get more uptravel.

Goatman · Apr 9, 2012

rockclimber said:
at full droop, the spring unseats about 2" thats why I'm looking to run a progressive spring. I'm leaning hard at the Currie's, Gerald/John's KOH EMC car was running them and gerald said the spring stayed seated for the entire stroke of their 14" kings.

Did they make their own custom springs? I've always thought the Currie progressive coil was the Deaver Jeepspeed coil, which we also ran in the KOH XJ, and there's no way it stayed seated for even 12" of travel. I thought Gerald said they had to play around a lot with spring rates.

rockclimber · Apr 9, 2012

Goatman said:
Did they make their own custom springs? I've always thought the Currie progressive coil was the Deaver Jeepspeed coil, which we also ran in the KOH XJ, and there's no way it stayed seated for even 12" of travel. I thought Gerald said they had to play around a lot with spring rates.

I'm fairly certain they are the savvy/currie 4" lift kit springs which have a slightly different spring rate than the standard currie progressive. I'll have to check with blaine next time I talk to him. I know they are an off the shelf part.

coilover spring rate issues

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