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Discussion Starter · #1 ·
I'm currently running a Rock Crawler 2.5" "Flex" system with Bilstein 5100s. I replaced the front LCAs and track bar with Synergy and also run a Synergy flipped drag link, tie rod, and sector shaft brace.

Rear track bar and control arms are stock, but using the RK geometry bracket that came with the original kit.

I'm running Tom Woods shafts, so no issues with pinion angles.

The Jeep rides and handles great, but I'm running a heavy rear bumper/tire carrier and only getting <1" lift in the rear. I often tow a ~1,800 lb camp trailer (about 150 lbs tongue weight). With the trailer, the Jeep sits lower than stock height in the rear (and about 3" lift in the front).

I run a few hundred pounds of gear in the back of the jeep (rear seats removed, plywood deck, 12v fridge and storage).

I'm running 35" tires with 4.88 gears along with MCE flares, so no issues with fender contact at full stuff.

I'd like a suspension setup that will retain (or improve) the great ride I already have, but better support the weight of the gear in the back and the trailer, and reduce the trailer "squat".

I'm looking for ideas on which components (short of a wholesale system swap) to replace/upgrade.

I like what I read about the AEV 3.5" dual sport setup, (I think I've read that they make some heavier rear springs to go with the kit for Jeeps that tow?)

My gut tells me that a set of 4 matched springs along with a rear trackbar and geometry bracket (maybe rear LCAs?) would do the trick. Then the next question becomes "which ones"...

Thanks in advance for the ideas.

Brent Christensen
 

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Air bags... Contact Airlift at 800-248-0892 and get their recommendation for their Airlift 1000 bags to match your springs. You might have to get them some measurements. I've been running their bags now for 3 years and with 5psi in them, you don't know they are there, but pumped up to 30psi and it levels me right out and supports the weight.

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Air bags, as Pressurized said. Any spring capable of dealing with that much weight is going to be overly stiff when you aren't putting that much weight on it. If you want springs, I would look at MetalCloak springs. They are multi-rate springs and they are better at coping with weight than most other springs. A set of MetalCloak 2.5" springs would be an option. But I think air bags are a better option. You can also get helper springs that take the place of the bumpstop jounces. They are sold by Timbren and help only when the Jeep is loaded down. But they are always there. Another lesser option would be Sumo Springs. MetalCloak has a version of them as well. They also take the place of the bumpstop jounces.
On a side note, how much bumpstop extension are you running up front. For a flipped draglink you usually need 3" of bumpstop extension. So most people don't run a flipped draglink for less than 3.5" of lift. If you don't have enough bumpstop extension at the right front corner you risk metal to metal contact when that corner is stuffed.
 

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You did also flip the track bar on the front. I would go with the air bags. I hate stiff springs. Also look into upgrading the brakes . Put brakes on the trailer if possible. With a 1800 pound trailer you want 10-15% of that in tongue weight for stability. When towing keep the tire PSI up. Good luck. The high CG and short WB is not your friend in towing. Go slow and look ahead.
 
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Discussion Starter · #5 ·
Thanks guys. I ran Airlift bags on my Tundra with 3" lift for towing a boat and I was really happy with them, but I thought I'd heard that putting them on a jeep decreases flexibility off road?

I definitely like the fact that you can use the air springs only when you need them. But that being said, my current setup is too low even when I'm not towing... (Measuring against factory settings, I've determined that I have a 0.57" lift on the rear pax side and 0.96" lift on the drivers side (before setting the trailer). The front, in contrast is nearly 3" so the Jeep isn't really level, even without the trailer.

With respect to the front end setup, I had the track bar and tie rod/drag link installed by Synergy (Polyperformance) and at the time they told me I was "on the edge" of flipping the DL so they recommended flipping it. (they said if I had 2.5" or less they would not have flipped it, but since I was a touch over 3" they flipped it). They also installed the bump stops and I just measured them - they are 4"at the front. It sure looks like I don't have much room to flex downward! This is also part of the reason that leads me down the path of considering a different (3.5") lift, as I've never really been happy with the RK stuff that was on the Jeep when I bought it. (the only things left being the springs and the front sway bar links)

With regard to trailering, I've got that pretty well dialed. The trailer has brakes and the setup stops very well both on road and off (even with the stock calipers and rotors and OEM pads). I run 30-32 PSI regularly and increase that to 34 front/36 rear when towing. (but then air down both Jeep and trailer when off road). Its an incredibly capable combo
 

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I put airbags in my 2015 JKR rear springs for towing and dirtbike carriers. I have the Rock Krawler 2.5" 2 door lift also. The bags stay at 5 psi normally. I pump them up to as much as 35psi when I have a dirtbike carrier on the back.

I bought the air lift 1000 universal air spring kit form etrailer AL60909 for my rock krawler springs. I measured the inside diameter, height, and coil spring pitch. There is a nice explanation on etrailer's site for measuring and picking the right part number.

 

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If I rock crawled more, I would not have installed the bags. They definitely increase the rear spring rates at their lowest allowed pressure. I've been considering removing them as I don't use a dirtbike carrier anymore. I recently installed rockhard4x4 oil pan and transfer case skid plates on my JKR, and that weight has put more of the factory rake on the jeep which I actually like. The highway handling seems to have returned to a more stock feeling too. I have avoided changing out my factory plastic rear bumper to a steel one due to the saggy ass syndrome on jeep lifts.
 

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Thanks guys. I ran Airlift bags on my Tundra with 3" lift for towing a boat and I was really happy with them, but I thought I'd heard that putting them on a jeep decreases flexibility off road?

I definitely like the fact that you can use the air springs only when you need them. But that being said, my current setup is too low even when I'm not towing... (Measuring against factory settings, I've determined that I have a 0.57" lift on the rear pax side and 0.96" lift on the drivers side (before setting the trailer). The front, in contrast is nearly 3" so the Jeep isn't really level, even without the trailer.

With respect to the front end setup, I had the track bar and tie rod/drag link installed by Synergy (Polyperformance) and at the time they told me I was "on the edge" of flipping the DL so they recommended flipping it. (they said if I had 2.5" or less they would not have flipped it, but since I was a touch over 3" they flipped it). They also installed the bump stops and I just measured them - they are 4"at the front. It sure looks like I don't have much room to flex downward! This is also part of the reason that leads me down the path of considering a different (3.5") lift, as I've never really been happy with the RK stuff that was on the Jeep when I bought it. (the only things left being the springs and the front sway bar links)

With regard to trailering, I've got that pretty well dialed. The trailer has brakes and the setup stops very well both on road and off (even with the stock calipers and rotors and OEM pads). I run 30-32 PSI regularly and increase that to 34 front/36 rear when towing. (but then air down both Jeep and trailer when off road). Its an incredibly capable combo
That is why you don't usually do a draglink flip at 2.5" of lift. You end up loosing suspension travel. You may be able to replace the 4" bumpstop extension with 3" bumpstop extensions, and that would add suspension travel up front. But you would want to flex the front suspension to make sure it clears with 3" of bumpstop.
Or you could go with more lift. But then you will likely find other issues. It is a slippery slope. Or you could simply remove the flipped draglink and extra bumpstop it requires. That would be the cheapest route. A flipped draglink just isn't required at 2.5" of lift.
I could see swapping the springs for MetalCloak 2.5" springs. If you go up to 3.5" springs you will be opening another can of worms, and further mods will likely be required. But that is up to you.
 

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I have a similar setup. 2016 JKU with 2.5 inch Rock Krawler lift with adj lower control arms on all four. I always thought it sat low in the back. I then got a 2000 lb camping trailer and it was close to the bump stops with about 180 lbs of tongue weight and gear in the back. I measured my actural lift empty and it was 3 inch in front and 1 3/8 in rear. This is after about 3 years of age. I though about air bags, but had issues off road on my prior XJ with them.

Decided to put 3 1/2 Rock Krawler springs in the back. I thought they would give me around 2 1/2 inch lift if they performed anthing like the original 2 1/2 inch springs. Of course they gave me a full 3 1/2 inches. So now the rear is 1/2 inch higher than the front plus the built in factory rake (which most lifts get rid of) of 1 inch, it looked like I was rolling down hill. I then went back and put 1/2 inch pucks in the front. Now I have 3 1/2 inch all the way around and it holds the tongue weight well. For some reason I think Rock Krawlers 2 1/2 inch rear springs have a lower spring rate.
 

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Discussion Starter · #10 ·
I have a similar setup. 2016 JKU with 2.5 inch Rock Krawler lift with adj lower control arms on all four. I always thought it sat low in the back. I then got a 2000 lb camping trailer and it was close to the bump stops with about 180 lbs of tongue weight and gear in the back. I measured my actural lift empty and it was 3 inch in front and 1 3/8 in rear. This is after about 3 years of age. I though about air bags, but had issues off road on my prior XJ with them.

Decided to put 3 1/2 Rock Krawler springs in the back. I thought they would give me around 2 1/2 inch lift if they performed anthing like the original 2 1/2 inch springs. Of course they gave me a full 3 1/2 inches. So now the rear is 1/2 inch higher than the front plus the built in factory rake (which most lifts get rid of) of 1 inch, it looked like I was rolling down hill. I then went back and put 1/2 inch pucks in the front. Now I have 3 1/2 inch all the way around and it holds the tongue weight well. For some reason I think Rock Krawlers 2 1/2 inch rear springs have a lower spring rate.
Thanks. I’ve thought about just adding Teraflex spacers to the rear but I’ve never liked the way spacers “preload” the suspension.

I might consider that RK trick with 3.5” springs, but I honestly don’t think the RK stuff is well made. At least their finishes suck (rust and chip off very quickly).

I’m wondering if swapping out just the springs for a 3.5” AEV SC kit and then adding the AEV rear geometry bracket and track bar (and possibly Synergy LCAs) might be the way to go. I think the Bilsteins that RK spec’d with the 2.5” kit are the same as the ones they used to spec for the 3.5” kit…


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Thanks. I’ve thought about just adding Teraflex spacers to the rear but I’ve never liked the way spacers “preload” the suspension.

I might consider that RK trick with 3.5” springs, but I honestly don’t think the RK stuff is well made. At least their finishes suck (rust and chip off very quickly).

I’m wondering if swapping out just the springs for a 3.5” AEV SC kit and then adding the AEV rear geometry bracket and track bar (and possibly Synergy LCAs) might be the way to go. I think the Bilsteins that RK spec’d with the 2.5” kit are the same as the ones they used to spec for the 3.5” kit…


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The AEV springs are decent, but not what I would call the best option for dealing with excessive weight. For that I would suggest the MetalCloak springs.
But, as has been mentioned, stiffer springs alone to deal with the additional weight may compromise the ride when not loaded down. Air bags would allow for extra weight capacity while not affecting the ride when not running heavy. Or helper springs would be somewhere in between.
 

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@sbsyncro I run spacers in every Jeep application I have. It's just like a motocross bike when adjust the rear spring to set ride height (droop). In the front of my LJ I have 1.5" spacers... It's not preload, it does not compress the spring further, it just raises the body. Measure the pinch seam to ground right behind the front tire and right in front of the back tire... Then add 1/4" and that's the spacer size to get you level. So if your rear is 3/4" less than the front at that pinch seam, you need 1" spacers in the rear. Easy, cheap and effective.
 
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Discussion Starter · #13 ·
@sbsyncro I run spacers in every Jeep application I have. It's just like a motocross bike when adjust the rear spring to set ride height (droop). In the front of my LJ I have 1.5" spacers... It's not preload, it does not compress the spring further, it just raises the body. Measure the pinch seam to ground right behind the front tire and right in front of the back tire... Then add 1/4" and that's the spacer size to get you level. So if your rear is 3/4" less than the front at that pinch seam, you need 1" spacers in the rear. Easy, cheap and effective.
Thank you. I think I’ll just do that then. A set of Teraflex spacers. Probably 2” on the passenger side and 1.5” on the driver’s side, but I’ll measure. (I’m making that assumption since the rear is currently 0.5” and 1” whereas the front is at 3” from stock, so that should put the rear at 2.5” and even it out in both directions)

I ran spacers on my Gen2 Tundra for a while before swapping to Icon coil overs & control arms and I remember that the ride was HARSH with those spacers. Perhaps it’s a whole different game with IFS and strut/coil over suspensions…(?)


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Thank you. I think I’ll just do that then. A set of Teraflex spacers. Probably 2” on the passenger side and 1.5” on the driver’s side, but I’ll measure. (I’m making that assumption since the rear is currently 0.5” and 1” whereas the front is at 3” from stock, so that should put the rear at 2.5” and even it out in both directions)

I ran spacers on my Gen2 Tundra for a while before swapping to Icon coil overs & control arms and I remember that the ride was HARSH with those spacers. Perhaps it’s a whole different game with IFS and strut/coil over suspensions…(?)


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Spacers do not change the spring rate. They only raise the ride height.
The advantage there is they don't increase the spring rate. The disadvantage there is they don't increase the spring rate. If you need more spring rate, they don't help with that.
They do what they do, and as long as you don't go crazy and run excessive amounts of spacer I really don't see a down side to them.
 

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IMO a set of MetalCloak springs if you have a heavy build. They are designed to handle a full armored and out fitted rig. My Jeep empty weighs almost 1000 lbs more than the day I picked it up. When I am loaded up and pulling the trailer it is another 1000 lbs being added. Here is a picture with the Jeep at the heaviest it has ever been. No issue at all on a 1200 mile move.

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I think another improvement to help with the towing manners would be to upgrade the rear track bar and brackets. I really like the Synergy upper rear track bar bracket brace. I would look into a strong bolt-on or welded lower bracket that raises the track bar 4"-6" inches and a very heavy duty track bar with a high durometer rubber bushing. A 2 Door will possibly run into clearance issues with 6" raised bracket but I believe 4 doors don't have this issue. A lot of people don't realize the benefit of raising the track bar to improve roll center and trying to get the track bar as level as possible at ride height to minimize axle shift during articulation. My favorite brands for track bars are Metalcloak and JKS but I'm sure there are other good ones but ask about the durometer of the clevite bushing in other brands. JKS uses one of highest durometer clevite bushings while MC uses a patented stiff articulating bushing.

I have only towed once and I was significantly overweight with my 2 door JK, It did great going through the mountain passes and I ran into a windy snow storm going to Aspen. I want to think that having the old 6" Metalcloak bracket and rear track bar along with the Synergy upper bracket kept things under control. I do drive my 2 door aggressively on the street and forest roads and it feels very stable and planted for a Jeep on 37s and 3.5" lift. Towing and encountering crosswinds can put a lot of lateral stress on the track bar and brackets.

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OP, how heavy more or less according to your calculations is you rear end ? and how old are those RK 2.5" springs?. Few months ago when i was researching coil springs to lift my rig i found a few threads from people saying the rear RK springs were a little on the soft side and they were not holding back a lot of weight. I'm talking about old posts i've found in 2013, 2015, 2016 etc. I wasn't interested in heavy rate springs so i started doing more digging as i liked the price on the RK springs and decided to buy them based on more recent posts, i went with the RK 1.5" coils myself, RK04186/RK04187 as of a few months ago.
I already had mods when i did the rears, so my Jeep butts is about 300lbs heavier than stock and with the RK 1.5" coils i have my butt is lifted 2" with respect to stock

I used this diagram to measure, basically from the edge of the bumpstop cup to the bumpstop pad
Font Line Parallel Circle Drawing

in my case,my stock numbers for the rear were 5" on both sides. with the RK 1.5" springs and 300lbs of weight in the rear (steel bumper, spare/carrier, toolbags/recovery gear,security enclosure etc, etc), my Jeep is at 7" in the rear on both sides. I don't know how much rear lift the RK 1.5 springs would have given me stock, i know the fronts one were 3" even, so i'd assume 2.5" perhaps
20211026_090122 by RAM RSM, on Flickr

If your rear is really that low it's possible you have old tired springs, maybe the spring rates were not that great before, maybe you have an insane amount of weight back there ?

Try a newer set of 2.5" springs as i'd think they changed the rate from years ago so you can start fresh at 2.5" and adjust with a small spacer, or go straight to 3.5" springs. My RK rear 1.5 springs measured 16 7/8', so according to their chart, the 2.5' are about 3/4" taller, and the 3.5's are 1.5" taller compared to the 1.5's. Again all this numbers are from their springs i bought brand new couple of months ago. They have 4 different flavors on spring height, in theory 1.5" and 2.5" have the same spring rate, i don't know if that changes on their 3.5" and 4.5" versions. Talk to RK to check.

RK04187$199.00 per pair1.5"17.043"5.596"
RK03101$199.00 per pair2.5"17.730"6.680"
RK02002$199.00 per pair3.5"18.590"6.730"
RK06014$199.00 per pair4.5"19.500"7.100"


You can always use spacers to get back to where is needed. I'm doing that with my RK 1.5" fronts. i got 3" stock with those, and after weight i went down to 2.25", (bumpers, winch, skids, sliders etc etc), so i have a 0.75" Daystar in the front now and went back to 3" with mods. The ride is super plush so i'm hanging into this springs for a while :)

I'll also upgrade the rear control arms to something with better bushings, Go with Clayton Overland + arms, Metalcloak, Synergy, Rancho, etc, any of the ones with DDB bushings, they're maintenance free like the stock clevite ones, but a lot stronger and flexy compared to those. I love the Giiros in the Claytons, i have a 7k lbs truck with those in the rear, have them in there for 2 years, set it and forget it, they flex really nice and their bushings are self centering and fully sealed. Also Clayton rear TB with the same Giiro bushings, but if you want to save some dove, Superlift with reflex bushings are a bit cheaper, that's what i have in the back of my Jeep, while i have the Clayton in the front. Having good bushings in the control arms and TB should tight up that but when loaded, asides of course from having good coil springs that can support the wight you have.

Have fun.
 

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Discussion Starter · #19 ·
Again, thank you all for the informative posts! Rob50lx you've got me drooling over the Synergy parts catalog again... A rear track bar and control arms are on my shopping list one of these days (once I finish a couple other things). rsmwrangler you got me motivated to get outside with a measuring tape and get a little dirty during my work day. Pressurized and GuzziMoto your knowledge continues to impress me every time I visit this site to research an issue and ask for help. The community would not be the same without you are resources. Thank you all!

For those curious, I'll post my numbers:

Based on information presented above (and other threads here on WF) I went ahead and measured everything again (rather than taking the word from a shop that worked on it a couple years ago). Here's what I'm showing:

FRONT

Automotive design Line Engineering Auto part Automotive exterior


Measurement "A"
DS shock measurement = 21.25 - 18.5 = 2.75" lift
PS shock measurement = 21.5 - 18.5 = 3.0" lift

Measurement "B"
DS spring perch measurement = 13.0 - 9.375 = 3.625" lift
PS spring perch measurement = 13.25 - 9.375 = 3.785" lift

Not sure why there is almost an inch of discrepancy between these two measurements... Perhaps its because I have a Rubicon?

REAR
DS bump stop cup to bump stop platform = 7.0 - 5.19 = 1.81" (versus non-Rubicon)
PS bump stop cup to bump stop platform = 6.785 - 5.19 = 1.60"

Interestingly, my pinch seams are the same front to back, so the Jeep is level. The driver's side is about 1/4" higher than the passenger side.

I have 2.5" of added bump stop in the rear (bolt on pad + puck)
There is 4" of bump stop added to the front (and only about 1" between the factory bump stop and the added pads).

I went ahead and ordered the airlift airbags - after measuring, I found that I needed 11" tall and 4" wide, so I went with kit # 60912. It was $102 shipped next day from Amazon. I figured that it is the most versatile (and easily reversible) solution. For those interested, the lookup table is here:

 

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Like everyone says, airbags. I too have Airlift ones. Love them. I’ve run the Rubicon with them if you are worried about hurting flex.

They keep things nice and level, and yes I have trailer brakes too. This was a few years ago with our pop up. 2x 100+ lb mutts and the 450 on the deck of the PuP. Towed flat and straight and probably 20k miles like that. Now close to 10 years later, those same airbags are still in there doing perfect for whenever I put a bike on the hitch carrier.

 
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