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School me: spring rates/lengths for coilovers

way over sprung and I would never recommend 16" shocks in front. you need to finish the rig, put one spring of known length and rate on each shock, and come back to us with relevant data.

buy your springs from a shock tuner not a salesman.
 
Discussion starter · #838 · May 23, 2015

ok 14"x 200 over 16"x 200's on the rear---only preload is compressing the springs onto the shock-- which ='s right around 1"---I'll update that measurement once I check my notes. trying to compress that combo on a 14" coil over by yourself with no tools isn't as easy as it sounds!!! I got one, but thankfully my son came and helped with the other--not sure how I got the one done.

I can't adjust this combo to my desired ride height at the moment, but I still need to load it with fluids, tools and such and hope I get some more compression

I barely and I mean I barely fit in the garage in fact I had to move so slow and reach up and push the garage door as far as it would go to slip in. So now I'm going to rig up my 1500lb winch to compress the springs, so I can get in and out easier(I hope). I could lower the tire pressure, but I'm at 20psi right now and I'm not sure I want to go less while driving it on the road? Anyone have any insight on that??

OK back to the garage.....
 
csutton7 said:
In my '48 Willys thread over on the other site I have a ton of info about how to set up, calculate, etc if one wants to go back to read it or I'll see if i can copy all of that info and somehow paste it on here.
Click to expand...

I remember your old thread and all the spring/setup info you had going on in there. If it wouldn't be too much trouble, moving that info to this site would be awesome!


Edit: Just saw your posts. Hell ya! :smokin:
 
Last edited:
You are welcome--it's a lot to decipher, but it can be done, you just need time to read, reread and read it again about a dozen times, Unfortunately, I don't remember most of it, but I do need to re-up myself because I need to get different springs for my rig and now it's easy to find here.
 
no way im going to read that vomit sutton posted. :flipoff2:

get springs your know the rates of fill out the sheet and check back.

unless you figure out the rates youre SOL. does your invoice say what rates they sent you?

also make sure the shocks have a charge in them - 200psi

cutnpasteintobrowser-https://docs.google.com/spreadsheets/d/13JqcO379dhaUPZegqnkC2e9reolzTT2c
 
So, using that crawlpedia link... thanks for that, was very helpful.

On my CJ I just linked the math comes out to looking way too light.


It's on 14"s, had 250 14s, and 150 16s on it cause that was what was on shelf. It sat too high with 0 preload. Threw 14" 200s on it thinking it'd lower it and would be able to get some preload but it's still 3" high even with 0 preload.

The math worked out 611 pounds at each front corner, wanting 6" shaft showing so that's 8" squat... right?

611 divided by 8 is 152.75.

So a 200 lower and 150 upper should be right... right?
 
NDCjeepsmith said:
So, using that crawlpedia link... thanks for that, was very helpful.

On my CJ I just linked the math comes out to looking way too light.


It's on 14"s, had 250 14s, and 150 16s on it cause that was what was on shelf. It sat too high with 0 preload. Threw 14" 200s on it thinking it'd lower it and would be able to get some preload but it's still 3" high even with 0 preload.

The math worked out 611 pounds at each front corner, wanting 6" shaft showing so that's 8" squat... right?

611 divided by 8 is 152.75.

So a 200 lower and 150 upper should be right... right?
Click to expand...

611 / 8 = 76.375, so you need a ~76 lb combined spring rate to have the springs compressed 8" at ride height if that 611lb figure is accurate.

Then when you stack springs, they combine into a reduced total spring rate. So a 150lb lower and 150lb upper would net you a ~75lb primary rate and be right in your target range, not accounting for installed angles and motion ratio stuff. The chart at the bottom of this crawlpedia page is a handy at-a-glance reference

Coilover Spring Rate Calculator (Dual Rate Spring Calculator)
 
AgitatedPancake said:
611 / 8 = 76.375, so you need a ~76 lb combined spring rate to have the springs compressed 8" at ride height if that 611lb figure is accurate.

Then when you stack springs, they combine into a reduced total spring rate. So a 150lb lower and 150lb upper would net you a ~75lb primary rate and be right in your target range, not accounting for installed angles and motion ratio stuff. The chart at the bottom of this crawlpedia page is a handy at-a-glance reference

Coilover Spring Rate Calculator (Dual Rate Spring Calculator)
Click to expand...
Right... the 152.75 was actually 611/8x2 since it's a double coil...

So per the link I was at that's not netting me what I really need?

Is there a downside to running two of the same rates?

I also just realized when I did the "measure the squat" way to determine weight they were charged. Should they be uncharged?

One hand says that will effect it, the other says it won't because it's squating them as of now so they're not so stiff that's its not showing me anything...
 
Ok, so I had time today to swap coils, go to a single, get it all to ride height and I'm thinking my math is screwed up, because the front appears wayyyyy too light. (Although I did push the engine way back into the cowl).

So far: 16 inch coils (16.125 actual) when loaded 14 inches on 300lb springs. (2.125 x 300 = 637.5 (650 + fluids call it 700). 700 ÷ 10.5 (squat) = 66.7 x 2 = 133.4 133.4 (dual spring rate) = 150lb lower, 100lb upper in front, unless I should go triple rate with 16" coilovers in the front.

Rear (14.125 unloaded) when loaded 11.5 inches on 275lb rate (found invoice). 275 x 2.625 = 722 (call it 1000, spare, rear seat, cooler, fuel missing) = 1000 ÷ 9.5 (rear squat) = 105. 105 x 2 = 210. 250lb lower 200 Lb upper.

Does that sound correct?

Motion ratio 44.375 ÷ 14.375 (3.08) if that makes a difference for the trailing arms.
 
NDCjeepsmith said:
Right... the 152.75 was actually 611/8x2 since it's a double coil...

So per the link I was at that's not netting me what I really need?

Is there a downside to running two of the same rates?

I also just realized when I did the "measure the squat" way to determine weight they were charged. Should they be uncharged?

One hand says that will effect it, the other says it won't because it's squating them as of now so they're not so stiff that's its not showing me anything...
Click to expand...

Ahh yep, that makes sense.

No big downside to running two of the same rate afaik, what it primarily effects is how much the spring rate steps up when the slider hits the stop collar. In that 150/150 example, you'd have 75 lb/in primary, and step up to 150 once you contact the collar. Then if you run stiffer lower springs, you'll obviously step up to whatever that higher rate is. I don't have the experience to offer a preference, but some of these guys might have better insight. The 200 lower and 150 upper would be close at ~87lb/in combined rate, but a little higher rate than the "ideal" math, so your ride height might end up a little tall once you set preload.

1Sinner said:
Ok, so I had time today to swap coils, go to a single, get it all to ride height and I'm thinking my math is screwed up, because the front appears wayyyyy too light. (Although I did push the engine way back into the cowl).

So far: 16 inch coils (16.125 actual) when loaded 14 inches on 300lb springs. (2.125 x 300 = 637.5 (650 + fluids call it 700). 700 ÷ 10.5 (squat) = 66.7 x 2 = 133.4 133.4 (dual spring rate) = 150lb lower, 100lb upper in front, unless I should go triple rate with 16" coilovers in the front.

Rear (14.125 unloaded) when loaded 11.5 inches on 275lb rate (found invoice). 275 x 2.625 = 722 (call it 1000, spare, rear seat, cooler, fuel missing) = 1000 ÷ 9.5 (rear squat) = 105. 105 x 2 = 210. 250lb lower 200 Lb upper.

Does that sound correct?

Motion ratio 44.375 ÷ 14.375 (3.08) if that makes a difference for the trailing arms.
Click to expand...

I'm not a guru at this stuff, but your math looks right. The suuuper light front spring rate is just due to wanting 10" of droop on a not-so-heavy vehicle.

Honest opinion though, if you think your rear weight may change by ~30-40% by the time your finished, it might not be time to be dialing in spring rates yet. That's a lot of variables left on the table. Any of that weight that ends up in front of the axle will add weight to the front springs, and any weight added behind the axle will pull weight off the front springs. A spare hanging off the tailgate being a good example, that could change the desired rates for both axles as it changes the F/R weight balance of the whole rig. Another note that might have been covered already, but in your initial pics with the rear at full squat, that angle of the chassis will change how much weight is sitting on the front springs. That might be corrected now that you've put springs on both axles, but figured worth mentioning
 
1Sinner do you have a pair of 100 pound coil springs you can find out the weight with? It makes the math for each corner much easier.
 
RunningProblem said:
1Sinner do you have a pair of 100 pound coil springs you can find out the weight with? It makes the math for each corner much easier.
Click to expand...
I'm thinking this too. May be easier to start over than continue chasing fuck all around since I measured with a charge and both coils
 
1Sinner said:
I don't, unfortunately.
Click to expand...
I’d suggest getting rid of the “ride height” stuff you’ve done and getting an accurate corner weight. AFTER you know the sprung weight of each corner you can start calculating spring rates and right heights. Doing it by setting ride height then calculating the spring compression isn’t the way you’ll want to do it. If you have a 30p pound spring it could work. The coilspring just won’t compress as much as a 100 pound spring.


Coilover Spring Rate Calculator (Dual Rate Spring Calculator)

Crawlpedia's spring rate calculator will help you find the correct primary, secondary, and tener spring rates for you IFS, trailing arm, or 4-link suspension.
www.crawlpedia.com
 
In my experience just doing this, u want the shocks charged when using spring to calculate corner weight. You will 100% have a different corner weight reading with charged vs uncharged shock.

Also preload should be set with limit straps installed, otherwise you may end up with more preload than you think. Limit straps are shortening shock travel to whatever amount you set. I found this info on accutune. Makes sense if you think about it.

I am currently at 175/200 in the rear and 200/250 in the front on my cj6. Rear is just about right, front is oversprung by an inch or so.
 
Scottie said:
In my experience just doing this, u want the shocks charged when using spring to calculate corner weight. You will 100% have a different corner weight reading with charged vs uncharged shock.
Click to expand...
Wouldn't the Nitrogen pressure support some of the weight, instead of compressing the spring in a linear, measurable manner?
 
Firstram said:
Wouldn't the Nitrogen pressure support some of the weight, instead of compressing the spring in a linear, measurable manner?
Click to expand...
Yes the nitrogen adds “spring rate” if you will. It made my rig sit .75 or so higher. If I had calculated with them already charged that would have been accounted for. Definitely have to bounce on it a little new shocks seems to be sticky.
 
i156sduyolhnel9cshem7&ep=v1_videos_search&rid=200w.gif


4 things
A. 16" shocks do not belong on the front of any vehicle, unless its a monster truck
2. shocks need a full charge of nitrogen (200psi, regardless of what the mfg says)
C. 1Sinner your front numbers are inline with what i would expect to see, your springs will bow and rub your shocks so accept that for what it is.
4. 1Sinner spring rate selection will be a challenge for you with them being that light and that long.
E. 1Sinner you are not ready for spring rate calculations until you are ready to drive the thing out of the shop, springs should be the last thing to purchase
F. the crawlipedia calculator overcomplicates a simple arithmetic problem, dont use it
G. keep it simple stupid, follow this procedure
- with the vehicle ready to leave the garage with the tcase in neutral​
- 200 psi of nitrogen in the shocks, with springs of a known length and rate on the shocks​
- adjust top adjuster nut to get the desire ride height​
- measure the following items​
- shock shaft showing​
- compressed spring lengths​
​

now time for the super complicated math portion
  • shock length - shock shaft showing = shock uptravel
  • spring static length - spring collapse length = spring travel
  • spring travel x spring rate = spring load
  • spring load / (shock uptravel + 1" for front OR 2" for the rear) = desired spring rate
  • desired spring rate is a guide
- i like 150lb split in rates, but in a lot of cases not feasible​
- id strongly advise not to drop below 150lb individual rate​

this will do all the math if you fill it out
cutnpasteintobrowser-https://docs.google.com/spreadsheets/d/13JqcO379dhaUPZegqnkC2e9reolzTT2c/edit#gid=1319103333
 
mobil1syn said:
i156sduyolhnel9cshem7&ep=v1_videos_search&rid=200w.gif


4 things
A. 16" shocks do not belong on the front of any vehicle, unless its a monster truck
Click to expand...
Copy, but, the geometry and towers have all been set up for 16's. Had this been mentioned or talked about through the course of the build and prior to ordering I would have likely made a change. Unless off road manners, or on road manners are terrible, they'll stay and I'll deal with them. If things don't work out and my hand is forced, I'll cross the bridge then. I don't have the money to throw multiple sets of coilovers at this project, due to some other issues I've covered in the park.

I appreciate the sound advice, and will continue towards completion and full build weight. Prior to finding final spring weight. This is why I started this thread, after all. I am not a coilover expert and this is my first build on coilovers and trailing arms. So I have a long way to go. No worries, I'll keep reading and researching.
 
1Sinner I didn’t know anything until I bought coilovers. Crawlopedia has a good website to do the spring rate math for you. Just find out the corner weight accurately and go from there.
 
I would Absolutely do what mobil1syn says, he knows a thing or two. There was a post a mile long on the old site from him and Dad.
 
SMI17 said:
I would Absolutely do what mobil1syn says, he knows a thing or two. There was a post a mile long on the old site from him and Dad.
Click to expand...
I'm not doubting his advice, at all. Again, I just can't afford a new set of 14s or 12s right now. Project is about to be put on hold due to a custody battle for my son.
 
1Sinner said:
Copy, but, the geometry and towers have all been set up for 16's. Had this been mentioned or talked about through the course of the build and prior to ordering I would have likely made a change. Unless off road manners, or on road manners are terrible, they'll stay and I'll deal with them. If things don't work out and my hand is forced, I'll cross the bridge then. I don't have the money to throw multiple sets of coilovers at this project, due to some other issues I've covered in the park.

I appreciate the sound advice, and will continue towards completion and full build weight. Prior to finding final spring weight. This is why I started this thread, after all. I am not a coilover expert and this is my first build on coilovers and trailing arms. So I have a long way to go. No worries, I'll keep reading and researching.
Click to expand...

dont take it personally, it was more of a general comment as i have seen a few builds recently using 16s. many moons ago i got all giddy and wanted all the travel too. it wasnt warranted and if i were to build another solid axle id be considering 12s with a little motion ratio.

1715656418871.png


1715656293635.png
 
mobil1syn said:
dont take it personally, it was more of a general comment as i have seen a few builds recently using 16s. many moons ago i got all giddy and wanted all the travel too. it wasnt warranted and if i were to build another solid axle id be considering 12s with a little motion ratio.
Click to expand...
That's fair, and it wasn't an affront, just stating my position.
 
My old buggy has 16 front and leafs rear. I built it with a cheap set of used 16s and didn't want to change my c/o mounts. It works, leafs make it stable/predictable buy I knew that 16s were way too much. Next rig will have 14 front and rear if not even 12s due to playing it motion rates
 
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