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Advanced Fabrication and Engineering For when your build is going off the charts. Wildly modified vehicles and straight up buggies welcome.

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  #1  
Old May 15th, 2005, 10:37
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Goatman Goatman is offline
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spring rates...corner loads...coilovers

OK, I did it. I got a set of 12" SAW coilovers for the front. Now I've been playing around charting various (more like numerous) spring combinations, and I have some questions. Ed?

I know I can figure my corner weight once I get the shocks mounted up, since the used coilovers I got already have springs, even a few extra sets (none, I'm afraid, that I can use). But, I'd like to have an idea ahead of time, and maybe at least get one spring that could possibly work. What corner weights have you guys come up with that have already done coilovers?

I've searched some, but haven't found conclusive answers. Who remembers the spring rates for RE 4.5" ZJ coils, or 8" Skyjacker coils? I'm trying to compare to determine the spring rate I think I'll like at ride height.

So far, here are a few of my thoughts. I want 5" of compression left at ride height. I want the secondary rate to kick in after 1" of compression from ride height. I want the primary rate to be as close as I can to get the desired ride height, so the preload at full droop is minimal. I want the total spring force to allow full articulation at 10.5" of compression, the last 1.5" is for the fast stuff.

I don't have Excel at home, so I can't play with Ed's spread sheet, but I've charted a bunch of combinations by hand, and the biggest problem I keep coming up with is blocking on the lower coil at full compression when it looks like I get the spring rates close. Now, I've been using 1200 lbs as a corner weight, because I have a bunch of stuff on the front of my rig, and going from what SeanP posted as his corner weights. As I've looked back through previous threads here, the couple of times corner weights are mentioned it's much lower than I'm figuring.
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  #2  
Old May 15th, 2005, 12:56
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Re: spring rates...corner loads...coilovers

Quote:
Originally Posted by Goatman
I don't have Excel at home, so I can't play with Ed's spread sheet
www.openoffice.org it's an open source (free) alternative to MS Office

Quote:
Originally Posted by Goatman
As I've looked back through previous threads here, the couple of times corner weights are mentioned it's much lower than I'm figuring.
Sometimes we forget the obvious, you are subtracting out un-sprung weight, right? (and half of all springs, shocks, driveshafts, links, etc)

Do you have your upper mounts figured yet? does it include a tube over the engine? can't wait to see pictures of that.
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  #3  
Old May 15th, 2005, 13:08
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Re: spring rates...corner loads...coilovers

Quote:
Originally Posted by BrettM
www.openoffice.org it's an open source (free) alternative to MS Office.
Actually, it's pretty easy to figure by hand, and I have it sort of graphed out so I can look at all of my various combinations at once.


Quote:
Originally Posted by BrettM
Sometimes we forget the obvious, you are subtracting out un-sprung weight, right? (and half of all springs, shocks, driveshafts, links, etc)
Of course. I didn't fall off the turnip truck.....I jumped.


Quote:
Originally Posted by BrettM
Do you have your upper mounts figured yet? does it include a tube over the engine? can't wait to see pictures of that.
I have the hoops bent, and generally where they'll go. It's not a simple thing to figure out where to put the stuff that's on the inside of the fender well, where the top of the shocks need to go. Moving that stuff is the biggest challenge of the project. I'll have to see if I think a tube over the engine will help much. It would be to add even more stiffness to the whole front end, it won't be needed to support the shock hoops since I'll tie into the tubing that is already running under my front fenders.
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  #4  
Old May 15th, 2005, 13:13
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Re: spring rates...corner loads...coilovers

Quote:
Originally Posted by BrettM
www.openoffice.org it's an open source (free) alternative to MS Office


Sometimes we forget the obvious, you are subtracting out un-sprung weight, right? (and half of all springs, shocks, driveshafts, links, etc)

Do you have your upper mounts figured yet? does it include a tube over the engine? can't wait to see pictures of that.

I used 12" Black Diamond coilovers. and they only have 2 springs available for them. I have a bolt in crossover not shown in the pics

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  #5  
Old May 15th, 2005, 13:17
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Re: spring rates...corner loads...coilovers

Quote:
Originally Posted by Goatman
I have the hoops bent, and generally where they'll go. It's not a simple thing to figure out where to put the stuff that's on the inside of the fender well, where the top of the shocks need to go. Moving that stuff is the biggest challenge of the project. I'll have to see if I think a tube over the engine will help much. It would be to add even more stiffness to the whole front end, it won't be needed to support the shock hoops since I'll tie into the tubing that is already running under my front fenders.
aw, common, 4 ft of 1.5" .095 wall only weighs 6 pounds
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  #6  
Old May 16th, 2005, 08:43
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Re: spring rates...corner loads...coilovers

Here's what I've come up with that looks like a workable choice. You guys who know about this stuff please tell me if I'm doing it correctly. I'm assuming a 1200 lb corner weight (if that's high I can adjust for it), and 12" travel shocks that have a length of 25.75" from spring seat to spring seat extended. I'm figuring a ride height of 7" (of compressed shock), and the transition to secondary rate at 1" above ride height.

Here are my spring force calculations using a helper coil, a 14" 325lb main, and a 10" 525lb tender. This gives me a primary rate of 200 lb/in and a secondary rate of 350 lb/in. The coil dividers are 1/4" thick each, and I'm assuming the helper is 1/4" thick collapsed. Block weight for the tender is 2840 and 2850 for the main, which is an estimate based on the Eibach chart, these would have to be Hypercoil springs, which I can get locally. Spring force is calculated starting at full shock extension.

0
0
200
400
600
800
1000
1200
1400
1725
2050
2375
2700

That would give me the desired ride height, and the spring force at 10.5" is 2213, which is where I would likely be when fully articulated. I've tried and tried to see if a 300 lb main would work, but it just won't, if I'm doing this correctly. From 1200 lb spring force at ride height, a 300 lb coil will block load before the shock is fully compressed......unless I change the transition point higher.
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Check out the TEAM Facebook page for the full story of our 2013 winning season: https://www.facebook.com/Team
Thanks to , Falken Tires, Bishop-Buehl Racing Engines, Ten Factory Axles, Brown Dog, Hooker Harness, BILSTEIN, Raceline Wheels, WARN, G&G Auto Repair/Off Road, Yukon Gear and Axle, Full Traction, Cal, Russ, James, and many, many others.
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  #7  
Old May 16th, 2005, 10:08
XJZ XJZ is offline
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Re: spring rates...corner loads...coilovers

Wasn't Paul working with Sway-A-way? What info does he have?
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  #8  
Old May 16th, 2005, 10:11
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Re: spring rates...corner loads...coilovers

Quote:
Originally Posted by XJZ
Wasn't Paul working with Sway-A-way? What info does he have?
I have what's left of all the SAW stuff. I'm still running them in the back, but the fronts are blown out and I'm not going to run them again. They are Big Bore reservoir shocks with pretty good valving, but still built for development and they're not holding up.
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Check out the TEAM Facebook page for the full story of our 2013 winning season: https://www.facebook.com/Team
Thanks to , Falken Tires, Bishop-Buehl Racing Engines, Ten Factory Axles, Brown Dog, Hooker Harness, BILSTEIN, Raceline Wheels, WARN, G&G Auto Repair/Off Road, Yukon Gear and Axle, Full Traction, Cal, Russ, James, and many, many others.
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  #9  
Old May 16th, 2005, 10:18
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Re: spring rates...corner loads...coilovers

btw....coil-over, mid-arm, 3-link. Very cool!!
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  #10  
Old May 16th, 2005, 11:11
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Re: spring rates...corner loads...coilovers

This question is in the wrong forum!

The Skyjackers are about 260 lbs/in.

The 4.5 ZJ's are about 240.

CRASH
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  #11  
Old May 16th, 2005, 11:39
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Re: spring rates...corner loads...coilovers

figuring a stock XJ at 3250 lbs (rough example)

55% on the front = ~1800 lbs

less 425 lbs for unsprung weight = 1375 lbs

or 687.5 per corner.

your figure of 1200 per corner = 2400 lbs on the front

less the stock estimate of 1375 leaves a difference of 1,025 lbs

Have you added 1,025 lbs of sprung weight to your front end (not axles and suspension) ? If not, maybe using 800 lbs would be more realistic.

Last edited by MaXJohnson; May 16th, 2005 at 11:47.
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  #12  
Old May 16th, 2005, 11:46
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Re: spring rates...corner loads...coilovers

Quote:
Originally Posted by CRASH
This question is in the wrong forum!

The Skyjackers are about 260 lbs/in.

The 4.5 ZJ's are about 240.

CRASH
I thought the SJ's were 240-250. For some reason I had figured mine with one coil cut off were about 260-265. I've also read that the RE ZJ's are 225......still curious what the real deal is. I see the guys who have run coilovers with a much lower primary rate and wonder how it really feels.
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Check out the TEAM Facebook page for the full story of our 2013 winning season: https://www.facebook.com/Team
Thanks to , Falken Tires, Bishop-Buehl Racing Engines, Ten Factory Axles, Brown Dog, Hooker Harness, BILSTEIN, Raceline Wheels, WARN, G&G Auto Repair/Off Road, Yukon Gear and Axle, Full Traction, Cal, Russ, James, and many, many others.
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  #13  
Old May 16th, 2005, 12:18
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Ed A. Stevens Ed A. Stevens is offline
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Re: spring rates...corner loads...coilovers

The XJ's I have looked at all load the springs between 700 and 800 pounds per front corner at rest height.

I expect your XJ to weigh-in close to 4800 pounds total, about 1600# sprung weight up front, and maybe a little more in the back. This puts about 3400 pounds of sprung weight and leaves about 1400 pounds in unsprung weight (tires & axles, and half the suspension links and springs).

Have you fitted a single rate spring on the front coilovers and measured the deflection at rest height (as long as the mounts will remain the same even the old shocks will work to determine the corner sprung weight)?
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  #14  
Old May 16th, 2005, 12:26
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Re: spring rates...corner loads...coilovers

Quote:
Originally Posted by Goatman
I thought the SJ's were 240-250. For some reason I had figured mine with one coil cut off were about 260-265. I've also read that the RE ZJ's are 225......still curious what the real deal is. I see the guys who have run coilovers with a much lower primary rate and wonder how it really feels.

Funny thing......if you measure the wire diameter as-shipped with thick powder-coating, the rate's end up about 10P/I higher than if you scrape the powder coat off!

I have the free length, OAL coil diameter and wire diameter at home for both, so I can check it. You can do the same with yours. Then, knowing that, you can take Ed's suggestion and figure how much the single rate SJ spring compresses under your Jeep's front load.
CRASH
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  #15  
Old May 16th, 2005, 13:54
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Re: spring rates...corner loads...coilovers

Imnot a pro at this but the MJ now has the black diamond XCL coilovers in the front. the spring ratings are 1600 light, 1800, med, 2050 heavy, and xtra 2250. This is measured as front end weight. I currently have the 1600 which came with them or 800 each wheel and even without the winch they are a bit too light. I have the nitro set at 200 psi but could go up to help with rebound. Im feeling the 900 to 1000 rate would be better.

Great thread Im learning alot!
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