Backend Bottoms out easily...

#1
Posted this type of question a few different ways on another forum, but didn't get much in the way of responses...figured folks on here may have a better understanding of running loaded.

The back end of my 07 JKU Wrangler seems to bottom out really easily when mildly loaded and /or towing a lighter load. Lift kit is 2" Mopar lift kit with Fox shocks. Using SumoSprings as progressive bumpstops ( works great BTW...foam spring about 3/4" longer than factory bumpstop). No rear tire carrier or aftermarket bumper...yet.

I am concerned about adding the additional weight of a tire carrier, Titan gas tank, AND carrying my usual overlanding load will exacerbate the bottoming out issue.

Rather than throw money at a guessing game, anyone have some thoughts? Anyone compare Mopar springs to Synergy? Do I need to get a revalve on my shocks? Go with heavier springs?

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#2
Not sure of that bumpstop setup? How can it "Bottom Out" or do you mean it's hitting Bumpstops? The bumpstop should prevent bottoming out... I believe?
 
#3
Not sure of that bumpstop setup? How can it "Bottom Out" or do you mean it's hitting Bumpstops? The bumpstop should prevent bottoming out... I believe?
Bottoming out occurs when going over bumps/dips at speed on freeway or high speed gravel roads and suspension runs out of compression. The rear end drops down after the bump/dip and bottoms out htting the bumpstops.

The sumospring is a bumpstop replacement that offer a progressive spring rate than the factory rubber bumpers and only come into play when suspension is at full compression...it reduces the impact of frame hitting axle or axle compressing into frame.

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#5
If you are already having this problem and you aren't done adding weight then you need new springs. If you were at your "normal" weight and adding extra weight for limited periods of times then air bags. If it was an occasional issue MAYBE adjustable shocks (not a real fix).
 

daveh

Adventurer
#6
I would look into a set of OME springs for the rear. They come in different ratings for load so make sure you speak to a knowledgeable reseller.


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Comanche Scott

Expedition Leader
#7
The stiffest of the stock JK springs /60 came on my Rubicon and they still felt mushy. I'm guessing your Jeep has /58 or /59 which is lighter and even more mushy feeling.
Going to an aftermarket spring made a big difference in our case.
Since your load will change dramatically, along with the spring change you may want to look at air bags as mentioned above.
I would look at both together, because even at minimum pressure they are additive in a progressive manner.
Teraflex has a nice rear bump stop setup, that will cushion the impact, but it doesn't affect sag with a load. This kit and the less expensive kit is designed for lifted Jeeps though.
https://www.quadratec.com/products/16197_1102_07.htm
 
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#9
Gents...I am not running factory springs...it has the Mopar 2" lift kit..which replaces factory springs with new ones and Fox shocks all the way around. I have not been able to tell if the springs in the Mopar kit have a rate higher or lower than stock.

My 07 Rubicon springs were shot at 70k...Jeep looked like a low rider compared to the newer ones, but I ran them another 30k or so and dealt with axles slamming into the factory bump stops...

My stock spring numbers were lower (don't recall) than what comes on the Rubi's now...so the 2" lift netted a huge delta (forgot to measure​).

@ Comanche What spring did you swap in?

I've run airbags before on the Jeep and was never really happy with the ride - somewhat unpredictable unloading behavior and the additional bounce became annoying after a few k miles into our trips. I've decided to purpose build this for overlanding and will use a heavier shocks/ springs. Just trying to determine which sets.
The stiffest of the stock JK springs /60 came on my Rubicon and they still felt mushy. I'm guessing your Jeep has /58 or /59 which is lighter and even more mushy feeling.
Going to an aftermarket spring made a big difference in our case.
Since your load will change dramatically, along with the spring change you may want to look at air bags as mentioned above.
I would look at both together, because even at minimum pressure they are additive in a progressive manner.
Teraflex has a nice rear bump stop setup, that will cushion the impact, but it doesn't affect sag with a load. This kit and the less expensive kit is designed for lifted Jeeps though.
https://www.quadratec.com/products/16197_1102_07.htm

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#11
So I bought a new 17 rubi the stock springs were awful. I added the pulloffs from my 12 which I traded. Added a ton of weight in the rear with it all. Stock springs I lost 2.5 inches of height in the rear. I put some rock krawler 1.5 inch triple rate springs on and I gained all my height back in the rear. I sit at stock height again. To give you an idea here is the pic of stock vs rock krawler springs.


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jscherb

Expedition Leader
#12
I've been running Air Lift 1000 air bags in my LJ for the past 6 years and in my LJ-based pickup for 8 years. I first put them in the pickup to deal with loads in the bed and I liked them so much I also added them to the LJ to deal with loads I carry when doing expedition travel. I typically run about 10 psi in them for everyday driving - that's the minimum I'd recommend to keep the bag in place inside the spring. When carrying a heavy load in the pickup I'll inflate them to 30 psi. For the LJ, I typically run 25 psi when I'm loaded for an expedition, which typically includes a second spare, cooler, baggage, etc., etc. At 10 psi with no load the ride is not affected, and at 25 psi with a load the ride is very similar to having no load on the stock suspension. I haven't noticed any ill effect on the trail, and usually have 20-25 psi in the system on the trail because of the extra load I usually carry.



One thing I'd recommend is installing an air gauge to monitor the pressure. One of the bags in the LJ developed a leak (Air Lift replaced it for free) but until I discovered the leak the bag was twisting in the spring and the twisting destroyed the air line.



I'm planning to install a set in the JKU as well, just haven't figured out where I want to put the gauge yet.
 
#13
I rant the #1000 Air lift bags in my springs on my Avalanche and they were pretty awesome. I decided to go all in which added more weight, so I swapped from my stock springs to Eibach Springs for a Hummer. Coincidentally, just prior to changing to those springs, on our last trip through DV, one of my bags developed a leak. With the new springs, I did not need to replace the air bags. Moral of the story - high quality, heavier duty springs make all the difference in the world.
//
I would look at OME Cargo Springs, I also think Eibach makes a heavier spring for a lifted JK, Moog might also have something.
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These are what I installed. My foot is a size 12.5.
IMG_1096.jpg
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Something else to consider - Fox 2.0 shocks stock valving are typically on the softer side for more traditional offroad performance. You may want to consider getting them revalved for the extra-weight associated with overlanding. When I did mine, they are completely custom for the extra weight and longer distances/durations: Fox 2.0 body, custom valving, 7/8" shafts, and bigger resrvoir. Something to consider.
IMG_1131.jpg
 
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Comanche Scott

Expedition Leader
#14
Gents...I am not running factory springs...it has the Mopar 2" lift kit..which replaces factory springs with new ones and Fox shocks all the way around. I have not been able to tell if the springs in the Mopar kit have a rate higher or lower than stock.

My 07 Rubicon springs were shot at 70k...Jeep looked like a low rider compared to the newer ones, but I ran them another 30k or so and dealt with axles slamming into the factory bump stops...

My stock spring numbers were lower (don't recall) than what comes on the Rubi's now...so the 2" lift netted a huge delta (forgot to measure​).

@ Comanche What spring did you swap in?

I've run airbags before on the Jeep and was never really happy with the ride - somewhat unpredictable unloading behavior and the additional bounce became annoying after a few k miles into our trips. I've decided to purpose build this for overlanding and will use a heavier shocks/ springs. Just trying to determine which sets.



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I've got the Mopar 3" lift (similar to the Teraflex 3" kit). It came with their lower priced Speed Bump setup.
Also running a Titan fuel tank, 35" spare on stock rim, along with 5 gallon water jug, and a rack that normally carries about 20lbs of fire wood.
Fully loaded for a road trip, it squats a bit more than 1" at the back to a more leveled out appearance. Unloaded it has a bit more than an inch rake.

It sounds like your rig will spend a lot more time loaded up, than unloaded. If that is the case a quality set of springs. I think OMU has 2" heavy duty lift springs that may be a good match. Might find someone running them, and see what kind of input you can glean from them.
You make a valid point on the the change of behavior for the air bags. I think it's worth the investment to valve the shocks for the springs/bags.
Hope this helps.
 
#15
So if I read the above responses, do most think I am undersprung in the rear? The amount of sag with the weight is relatively minor. I haven't measured it yet since it didn't seem all that bad. Next trip I will try to find some scales and will weigh it.

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