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Old 11-21-2019, 01:37 PM
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How to calculate needed rear coil spring for built-out rig

I've got the 2" Mopar lift with Fox shocks on my 2014 JKU. With all accessories, including massive rooftop tent and fully loaded rear compartment with fridge and cabinet build-out, I'm sitting right at 6600 pounds total ground weight. Front looks and feels fine, still 2-3" of lift. The rear however is severely compressed, and on a recent month-long trip, I was hitting my bump stops in the rear with even the most minor of road bumps, dips, etc. When articulated on a rock or something to level the rig for camping, it would just sit on the bump stops period.

I can't seem to find Mopar's rating for the "heavy duty" rear coil spring that comes with that kit (I think it's part# by itself is 68004459AA), nor has my Googling been successful in figuring out what rating I *should* be looking for to retain about a 2" lift with that weight. Any suspension kings out there have the answer?

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Old 11-21-2019, 01:51 PM   #2
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There is no mopar 2" kit that will give you what you want. You are heavy enough you probably should look at some rear TF outback springs.
https://teraflex.com/shop_items/jk-4...ck-spring-pair
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Old 11-21-2019, 02:04 PM
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Yeah the Mopar 2" are clearly coming up short (pun intended). But without knowing the ratings, how can I make any comparison before buying and installing? Where are the actual specs on the spring ratings? I am hoping for something more accurate than "heavier" duty. I'm also guessing that comparing the numbers will also be more informative when determining what comfort will be sacrificed when the vehicle is empty?
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Old 11-21-2019, 02:07 PM   #4
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Originally Posted by Nafai View Post
Yeah the Mopar 2" are clearly coming up short (pun intended). But without knowing the ratings, how can I make any comparison before buying and installing? Where are the actual specs on the spring ratings? I am hoping for something more accurate than "heavier" duty. I'm also guessing that comparing the numbers will also be more informative when determining what comfort will be sacrificed when the vehicle is empty?
I have never seen the spring rates published anywhere for the mopar 2" coils. @Pressurized has a pretty extensive list of spring rats for various springs but I think the mopar coils even escaped his data bank.
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https://www.wranglerforum.com/f314/y...i-2192385.html
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Old 11-21-2019, 02:11 PM   #5
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Would this be a use case for air bags which you can adjust based on your load?
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Old 11-21-2019, 02:26 PM   #6
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Quote:
Originally Posted by jadmt View Post
I have never seen the spring rates published anywhere for the mopar 2" coils. @Pressurized has a pretty extensive list of spring rats for various springs but I think the mopar coils even escaped his data bank.
I was told by a Mopar rep to expect an 8% to 10% increase over stock... So that's not a lot and not very specific...

I'd try a set of the JKS progressive rate rears. They are 185/225 which should be high enough to cover that much added weight.
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Old 11-21-2019, 05:46 PM
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Hadn't thought about air bags, hrm. Thanks for all the advice. I've reached out to a few progressive / dual rate coil manufacturers for their suggestions.
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Old 11-21-2019, 06:14 PM   #8
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You need to find a set of scales. Load the jeep up and get a weight of the rear axel. This will help the spring guys get you whet you need.
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Old 11-21-2019, 06:31 PM   #9
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You are going to need to move to a company that sets there spring height based on fully equipped rigs. AEV and MetalCloak are 2 such companies. My 2 door hits 5800 lbs when I head out, 6000 if I am pulling the trailer. here are a couple of pictures, empty and loaded. In fact in the loaded picture I am probably over 6000 lbs.

The other thing you have to start worrying when getting to this weight is the axles. Assuming you have 44's they are rated at 2750 for the front and 3200 for the rear. I know I don't want to go much heavier with out upgrading axles.
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Old 11-21-2019, 06:45 PM
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Good to know. I've got Dana 30 (2770 lbs supposedly) front and Dana 44 (3500 lbs?) in the rear. Metalcloak was top on my list simply from the tech essays they post in forums on stuff like this, and I am really happy with the build quality of a few of their non-suspension parts I have. I'll post back with their comments and check out AEV as well. I thought Dobinson might also be a good choice, but can't find confirmation that they set based on full equipment or not.
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Old 11-21-2019, 06:50 PM   #11
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Originally Posted by Nafai View Post
Good to know. I've got Dana 30 (2770 lbs supposedly) front and Dana 44 (3500 lbs?) in the rear. Metalcloak was top on my list simply from the tech essays they post in forums on stuff like this, and I am really happy with the build quality of a few of their non-suspension parts I have. I'll post back with their comments and check out AEV as well. I thought Dobinson might also be a good choice, but can't find confirmation that they set based on full equipment or not.
my rubicon recon has D44 front and rear and the heavier front D44 at that and gvwr is 2775 and 3200lb so doubt your rear is 3500lb. Check out OME as well. Most heavier springs are going to give you a fair amount of lift if that is a concern. I think OME has heavy 2-2.5 lift coils. OME also is good about giving spring rates.
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https://www.wranglerforum.com/f314/y...i-2192385.html
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Old 11-21-2019, 06:57 PM   #12
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Quote:
Originally Posted by Nafai View Post
Good to know. I've got Dana 30 (2770 lbs supposedly) front and Dana 44 (3500 lbs?) in the rear. Metalcloak was top on my list simply from the tech essays they post in forums on stuff like this, and I am really happy with the build quality of a few of their non-suspension parts I have. I'll post back with their comments and check out AEV as well. I thought Dobinson might also be a good choice, but can't find confirmation that they set based on full equipment or not.
Look on you door, it will give you front and rear vehicle weight limits. Of course it is really hard to find the actual limits of the axle.
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Old 11-21-2019, 07:32 PM
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Interesting, I thought the numbers on the door were taking stock coils into account, never noticed they were labeled GAWR. :/ Dana 44's list a max of 3500, but I guess that is given certain configurations, and this would indicate that the 44HD as kitted out in my Jeep is only 3200.

Guess it's time to find some place that can weigh per axle or wheel.
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Old 11-22-2019, 01:28 AM   #14
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Interesting, I thought the numbers on the door were taking stock coils into account, never noticed they were labeled GAWR. :/ Dana 44's list a max of 3500, but I guess that is given certain configurations, and this would indicate that the 44HD as kitted out in my Jeep is only 3200.

Guess it's time to find some place that can weigh per axle or wheel.
That weight is based on tires also. As I said I have not been able to find the actual weight the axles can hold.
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Old 11-22-2019, 02:52 AM   #15
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You won't find an apples to aples comparison for springs from different manufacturers. Most manufacturers springs will not be up to the job of supporting the weight that you're running because you're about a thousand pounds past GVW. Old man Emu makes three different 2.25" lift coils for the rear of your JK. I would suggest going with the heaviest set they sell which is a 2620. Teraflex has a set of overlanding springs that are stiffer, but they're taller than your current lift so they won't work. Proggressive springs won't help either if your Jeep is constantly loaded fairly heavy. They'll just compress the lighter spring rate end of the coil all the time and that's no help at all. I've had air bags and they're okay if you spend most of your time light with an occasional heavy load. They're not really designed for a consant load and that's where using the correct spring rate comes in. ARB has a list on line of their springs and spring rates so you can at least compare what they offer. Or you could always put that fat girl on a diet which would help out with engine and transmission wear, axles, mileage, cornering, braking and suspension. I realize it's really easy to overload a Jeep with accessories. Mine is currently 5055 lbs without my fat butt in the seat. I've got to be really careful with my choices to stay under GVW.
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Old 11-22-2019, 12:46 PM
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Proggressive springs won't help either if your Jeep is constantly loaded fairly heavy. They'll just compress the lighter spring rate end of the coil all the time and that's no help at all. I've had air bags and they're okay if you spend most of your time light with an occasional heavy load. They're not really designed for a consant load and that's where using the correct spring rate comes in.
When I'm not camping, it's pretty empty. The rack and rooftop tent stay on, as do the front/rear bumpers and winch. But inside it's passenger friendly and the fridge is in the garage. That's making me lean towards progressive/dual rate.

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Or you could always put that fat girl on a diet which would help out with engine and transmission wear, axles, mileage, cornering, braking and suspension. I realize it's really easy to overload a Jeep with accessories. Mine is currently 5055 lbs without my fat butt in the seat. I've got to be really careful with my choices to stay under GVW.
I don't really see where I could realistically change things to reduce weight unfortunately. I'm not taking day trips off-roading, we go bush for weeks at a time. I don't bring superfluous accessories, everything is used, daily. Fire extinguisher probably being the single exception :P.
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Old 11-22-2019, 12:53 PM   #17
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do you carry passengers with you? if not back seat weighs about 80lbs.
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Old 11-22-2019, 12:56 PM
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do you carry passengers with you? if not back seat weighs about 80lbs.
Not always, but occasionally. Back seats are currently out; with the Wet Okole covers, I weighed a 90# savings when removed. ╭( ・ㅂ・)و
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Old 11-22-2019, 09:05 PM   #19
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I've got a fairly heavy overland rig myself with a roof top and full kitchen setup. Currently running a 2 1/2" JKS lift which I did see about an 1" to 1 1/2" sag when fully loaded down. I ended up buying JKS rear adjustable coil spacers to fix the issue this summer. I just ordered a Currie 44/60 setup which I'll be installing this winter and thinking about swapping the springs when I change axles, but just not sure what springs to try.... I'll be following this thread closely!
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Old 11-22-2019, 09:57 PM   #20
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The Rubicon Express springs are high rate and the Clayton's are the highest I've found. Both are much higher than the OME's.

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