Difference between short and long arm lift? - JeepForum.com

 
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post #1 of 4 Old 12-03-2009, 06:01 AM Thread Starter
DocJake
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Difference between short and long arm lift?

I see both short and long arm lift kits. Can someone tell me the differences? Seems the higher lifts need longer arms? What effect does lifting have on the arms, and how does the short vs long affect dynamics and ride?

Cheers,

Doc


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2009 Wrangler JK Deep Water Blue 2/door, Auto Soft Top
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2.5" RC Coils/1" MORE-BL/3/4" Levellers/Skyjacker Hydros Shocks/JKS 2" Bumps
17" AEV Argent Pintlers/34.4" GY Duratracs
Rugged Ridge XHD Modular Bumpers, locking ends, grill loop
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post #2 of 4 Old 12-03-2009, 08:16 AM
Xtremjeepn
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My thoughts on a long arm for the JK.


There is some serious "marketing hype" left over from the TJ bleeding into what is right and wrong on a JK.

A TJ came stock with 30" tires as the largest size and the stock control arms are ~16" long. The JK control arms are 22.619" long and fits 32" tires stock. That is a 41.4% increase in control arm length. Which is not the only variable that is different. The mounts for springs, control arms etc on the JK are all totally different than on a TJ. What all this means is that what was NEEDED on a TJ is not the case on a JK.

To fit 35s on a TJ you needed ~6" of lift if done with all suspension and no trimming. This put a HUGE angle change on the 16" arms. To run the same 35" tire on a JK you need 2.5-3.5" of lift. Which is not a major change to the almost 23" arms. Even at 4.5" inches of lift it is still not that larger of a change. At 4.5" of lift the % of angle change is more equal to a TJ with a 2" lift.

As long as you are using the stock frame mount location a stock length arm is going to put your axle dead center in the wheel well and bump stop at full compression. That is what it is supposed to do. That is why they look slightly off set forward(in the rear) and reaward(in the front) when lifted.

The "Mid-Arm" rear arms like the RK are great for putting the wheel back center at rest, but when fully compressed the axle and tire are going to be offset of the bumpstop and sit rearward in the wheel well. Not a huge issue, you just need to be aware of it and adjust your bumpstop location and rear bumper accordingly. If not you could be in for a surprise at full stuff. (especially if running fast down a fire road after a trail).

"long arms" on some of the kits make me nervous. They mount the upper arms outside the frame rails which is not proper geometry for good handling. The arms need to come closer together. Which would require relocating the gas tank, or comming completely center .

The other issue I see is that some of them take the long lower frame mount and move it UP on the frame rail. This is great for clearance but you just increased the angle again from the stock point. (sometimes by 8"+) which negates the point of the long arms. (or would require even longer arms at that point).


Just for the hell of it I put an angle finder on my control arms with 4.5" of lift on my JK (stock arms) and on the 6" long arm kit of Stogie25 TJ. The angle was the same.

I just don't think a long arm does you any good on a JK until you are at 6+ inches of lift and at that point you are talking 40"+ tires.

Cole Ford
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post #3 of 4 Old 12-03-2009, 09:49 AM Thread Starter
DocJake
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wow..thanks for the comprehensive info on arms! It's reassuring since there are always the manufacturers of this stuff that inject a measure of insecurity and doubt over safety issues, unless of course, you buy their stuff. In any event, my total height would be at around 3.25" to 4.5" in the next year depending on how I configure it. I may also use an angle measure when its done, just out of curiosity. I know that after 3", the lifespan of the rear shaft gets dicey. Some here seem to have run over 4" for years of harsh treatment, while others were doomed after a year. As for a trackbar, I'm using my stocker right now. I took measurements from the inner edge of each wheel to the frame and was at most, an 1/8" off center. I can't see using a longer bar to correct for 1/16". If I go longer to correct the center with springs compressed, then its off center at rest. Not sure I can reason that.

Cheers,

Doc

The easiest way to find that missing socket wrench is to buy a replacement

2009 Wrangler JK Deep Water Blue 2/door, Auto Soft Top
Automatic/3.73
2.5" RC Coils/1" MORE-BL/3/4" Levellers/Skyjacker Hydros Shocks/JKS 2" Bumps
17" AEV Argent Pintlers/34.4" GY Duratracs
Rugged Ridge XHD Modular Bumpers, locking ends, grill loop
JKS Links/XHD Modular Bumpers/Locking End Units
SB-XCR8 Winch

http://theadirondoc.blogspot.com
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post #4 of 4 Old 12-03-2009, 09:52 AM
Xtremjeepn
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This is a good read too if you have not read it.


http://www.aev-conversions.com/12thi...lve_things.pdf

Cole Ford
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