RK spring spec vs MC vs ?

[wfo9]

I'm shopping for springs in the 2.5" lift range..

I recently installed a MC 3.5 gamechanger setup on my JLUR..

I'm not happy with the height.. It's too tall for my liking and a bit stiff.. The build is pretty light overall as I have mostly aluminum armor... Feels like it came out at at least 4.5" of lift. I've got 37s (which feel way more like 35s BFG KM3s) lot of clearance for the tires.

Anyway, considering the MC 2.5 springs (for JLU) or possibly RK or others.. I noticed RK claims triple rate.

What I'm looking for is specs on the RK springs that I cannot find (Free length fully compressed length) I want to make sure they will fit with my shock lengths.. Also does RK use specific isolators up top for their springs in front?

Any Intel greatly appreciated. The jeep feels over sprung at the moment (if that description makes sense).

Should probably just go with the MC springs, but figured I would at least consider RK or some other option..

MC lists 21.75" free length for the 2.5 front.. 19" for rear. My 3.5 fronts are listed at 22" and already pretty loose on full articulation up front.

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[hockeynut258]

Looks like you are on the same track as me. I got close to 5” from MC 3.5 springs. MC wasn’t much help. They asked for specific measurements. I was 1” above their jeeps at the shop but they left it at that. The ride was very rough too. Between the poor ride and resistance to help I didn’t want to roll the dice on MC 2.5 springs.

I was originally thinking RK springs too but went synergy because they have longer free length. RK said I would have to use limiting straps and didn't want to do that and synergy said no problem.

From RK website for 3.5 lift kit:
“Shock Notes:
Generic Front Shock Length – 17.8” Collapsed/ 29.3” Maximum Extended
Generic Rear Shock Length – 18.3” Collapsed/ 30.3” Maximum Extended”
https://rockkrawler.com/jlu-3-5-inch-x-factor-no-limits/

Synergy posts their spring lengths on their website. https://www.synergymfg.com/synergy-jeep-jl-jlu-rear-lift-coil-springs.html?category_id=4981

Im running bilstein 8100 bypass which have 32” rear extended length.

Synergy 3” front and 4” rear work perfect and ride about level at 4” measuring shock mount to mount. The ride is MUCH better than MC. MC springs I could feel every pebble on the road even with my shock compression at full soft.

I have a lot of measurement data i can share if it’ll help.

 

[wfo9]

Looks like you are on the same track as me. I got close to 5” from MC 3.5 springs. MC wasn’t much help. They asked for specific measurements. I was 1” above their jeeps at the shop but they left it at that. The ride was very rough too. Between the poor ride and resistance to help I didn’t want to roll the dice on MC 2.5 springs.

I was originally thinking RK springs too but went synergy because they have longer free length. RK said I would have to use limiting straps and didn't want to do that and synergy said no problem.

From RK website for 3.5 lift kit:
“Shock Notes:
Generic Front Shock Length – 17.8” Collapsed/ 29.3” Maximum Extended
Generic Rear Shock Length – 18.3” Collapsed/ 30.3” Maximum Extended”
https://rockkrawler.com/jlu-3-5-inch-x-factor-no-limits/

Synergy posts their spring lengths on their website. https://www.synergymfg.com/synergy-jeep-jl-jlu-rear-lift-coil-springs.html?category_id=4981

Im running bilstein 8100 bypass which have 32” rear extended length.

Synergy 3” front and 4” rear work perfect and ride about level at 4” measuring shock mount to mount. The ride is MUCH better than MC. MC springs I could feel every pebble on the road even with my shock compression at full soft.

I have a lot of measurement data i can share if it’ll help.

Excellent info.. I'll look into the synergy springs.. I'm blown away by how tall my MC lift came out.. 3.5" is a complete misrepresentation IMHO. I wish they would provide the spring rates and where the transitions are... RK does not even publish free length (but those shock lengths do seem to indicate 30" like MC rocksports would be too much)

One of my front springs has already shifted one time in the upper isolator after full articulated droop. Strange because I should be well within the envelope of the MC travel range, but it gets tricky with articulation considered. My shocks (Fox) are very close to the Rocksport advertised travel, but I'm not using their outboard shock mount upfront (I'm using the EVO one) So I should be about 1" less on droop (30.5 vs 31.5) and about .5" higher up on compress.

 

[GATORB8]

I don't have free length measurements except my MC 3.5s, which seem to match what you're listing.

There is an old thread with spring rate listings if it helps: https://www.jlwranglerforums.com/forum/threads/spring-rates.16491/post-1004928

Front / Rear​

​

JLU Sport : 117 / 172​

JLU Rubi : 125 / 174​

Mopar lift : 132 / 181​

Synergy : 120 / 175​

Teraflex : 140​

RK 2.5 : 137 / 175​

RK 3.5 : 140 / 185​

EVO Soft : they wouldn't tell me​

Metalcloak: they wouldn’t tell me​

 

[GATORB8]

Found your free length for front 2.5 RK's 20.5" per post below.

https://www.jlwranglerforums.com/fo...n-information-chart-matrix.66591/post-1857858

 

[srt20]

Recently installed MC 2.5 GC on JLUR. It raised my JLUR approx 4" front and back.
I have aluminum front bumper with winch, fairly heavy Roam sliders, OEM plastic rear bumper. Aluminum roof rack and awning on top. All 5 tires are BFG KO2 35x12.5x17. Tires were on before lift, so they are not part of the 4" raised.

Ride is stiffer than OEM, but not excessive IMO. My wife has no issues with ride, but I did used to own a 2500 Dodge diesel that rode like a dump truck.

Just a comp for 2.5" MC springs.

 

[wfo9]

Recently installed MC 2.5 GC on JLUR. It raised my JLUR approx 4" front and back.
I have aluminum front bumper with winch, fairly heavy Roam sliders, OEM plastic rear bumper. Aluminum roof rack and awning on top. All 5 tires are BFG KO2 35x12.5x17. Tires were on before lift, so they are not part of the 4" raised.

Ride is stiffer than OEM, but not excessive IMO. My wife has no issues with ride, but I did used to own a 2500 Dodge diesel that rode like a dump truck.

Just a comp for 2.5" MC springs.

Mine started out as an XR rubicon so hard to say what lift I got from MC.. But the 3.5 feels super tall. My jeep has similar parts as yours (except I have a aftermarket steel rear bumper but it is only 40lbs, and I would say it is at least 5" taller from just suspension with the MC 3.5".. The 2.5 seemed much more reasonable.. But I'm just not thrilled with the MC springs. Not terrible, but the jeep feels over sprung for the weight I typically have in it. Probably worse when I put the soft top on. I wish they would advertise the spring rates etc.


So many drivetrains etc.. this concept of X amount of lift.. Is getting kind of dumb.. There must be 15+ combinations of basically stock jeeps with all the different setups between etorque and non etorque plus all the engine choices and 2 vs 4 doors....

I've done several coil over setups for 4 link type setups and it's super easy just to put a known spring rate on and get your corner sprung weights.. Then you can pick the right spring combo to get into your desired ride height.. That works because you have two springs on each and you know the exact lengths of each and it becomes a simple calculation in a spreadsheet.. Would be a little more tricky with a dual rate single coil but should still be doable if they simply tested the coil and published the numbers (free length and total weight down to solid).

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