Long arm VS short arm
Former Vendor
Joined: Oct 2012
Posts: 1,615
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From: Newton, NJ
A general rule of thumb about control arms is the more parallel to the ground they are the better. Although at lower suspension heights they may hit larger rocks, long arms reduce stress on the rest of system and generally will give you a nicer ride than short arms with the exact same suspension set up. A high clearance mid arm system will give plenty of flex and with adjustable control arms you can correct the caster which is a very important part of the geometry of a jeep suspension.
Last edited by Smashboogie 4x4; Jan 13, 2013 at 10:08 AM.
JK Super Freak
Joined: Dec 2009
Posts: 1,695
Likes: 3
From: Texas
For long travel suspensions you want long arms. The long arms, among other things, will limit the fwd to back movement of the axle during up-down movement. An easy to picture this is to draw two concentric circles, one a two inch and one a five inch. If you move 1 inch (1/2" up and down) you will see how far left and right you move on the small circle versus moving 1 inch (1/2" up and down on the new circle cause wheel travel is only one inch) on the big circle. If you are lifting or dropping one tire you will shift one side back and not the other which will help induce some friction leading to binding at some point.
JK Junkie
Joined: Mar 2011
Posts: 2,145
Likes: 4
From: Israel
A general rule of thumb about control arms is the more parallel to the ground they are the better. Although at lower suspension heights they may hit larger rocks, long arms reduce stress on the rest of system and generally will give you a nicer ride than short arms with the exact same suspension set up.
I accept that the more horizontal the arms are the better. I don't accept the "nicer ride".
I tried a few 4" lifted Jeeps, with both short and long arms. Without exception, relatively soft coils and properly valved shocks always influenced the ride much more than arm length.
My previous JKU had air springs and short arms. On a specific trail, where I could comfortably do 50 mph, other Jeeps "rearranged" their drivers' bones – including Jeeps with long arms.
My point is that, up to 4" lift, there's no advantage in long arms. 8" lift is another story.
A high clearance mid arm system will give plenty of flex and with adjustable control arms you can correct the caster which is a very important part of the geometry of a jeep suspension.
It feels as nice as similar JKUs with the same suspension but with long arms. 4" lift, at least according to my experience, is not enough lift for long arms to make a meaningful difference.
The only way to make it even softer, without changing much, would be the EVO bolt-on coilovers.
What really improved my Jeeps' ride has nothing to do with coils, shocks or arm length:
The rear axle moves from side to side with every irregularity on road or trail. This causes directional instability – constant small corrections with the steering wheel. (This lack of directional stability is even more pronounced in a 2-door.)
I installed Full Tractions' CRC, which replaces the rear radius arm and completely eliminates the sideways movement of the axle. The improvement is remarkable.
JK Junkie
Joined: Mar 2011
Posts: 2,145
Likes: 4
From: Israel
This is what I mean regarding the benefit of long arms for taller lift:
If 'A' represents 4" lift, the short arm would behave nice enough to not give a long arm a meaningful edge.
However, if the lift is doubled to 8", the the short arm now has to go down to 'A1'. It is too far from horizontal.
The axle is drawn back too much.
In this case, of 8" lift, a long arm would be a must. It will have a smaller angle relative to the frame, and the axle wouldn't be drawn back so much.
For most of us, there's no need for more than 4" lift, and short arms are perfectly good for this lift, provided that everything is tuned right.
(But then, everything should be tuned right for long arms as well...)
If 'A' represents 4" lift, the short arm would behave nice enough to not give a long arm a meaningful edge.
However, if the lift is doubled to 8", the the short arm now has to go down to 'A1'. It is too far from horizontal.
The axle is drawn back too much.
In this case, of 8" lift, a long arm would be a must. It will have a smaller angle relative to the frame, and the axle wouldn't be drawn back so much.
For most of us, there's no need for more than 4" lift, and short arms are perfectly good for this lift, provided that everything is tuned right.
(But then, everything should be tuned right for long arms as well...)
Last edited by GJeep; Jan 13, 2013 at 03:44 PM.
JK Freak
Joined: Oct 2008
Posts: 524
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From: Yucaipa, ca
You'll hear a lot of things, including myth or misconceptions.
Yes, people install long arms on 4" lifted Jeeps. Why? They think it helps, and IMHO they're wrong.
Some people even tend to believe in the mod they did so much, that they would actually feel an improvement which isn't there.
For "high end" lift, say 8" or 10" for instance, the geometry of short arms wouldn't work right, and long arm are needed.
4" lift is just not enough for long arms to make a true Difference.
JK Junkie
Joined: Mar 2011
Posts: 2,145
Likes: 4
From: Israel
e.g. lift, coils, shocks, tire type & rating, tire pressure, bushings -- is everything similar ?