Long Arm Lifts vs. Short Arm Lifts

discussion like this and my understanding of suspension geometry.... although elementary compared to some on this forum is the reason I am in process of removing the RC long arm "upgrade" (installed by PO) on my TJ and converting to a Currie/Savvy 4" kit... Gonna get my short arms setup well and then see if my skill grows to the point I need the mid arm setup. If anyone has a bone stock TJ file for the calculator I would be grateful if they could send it to me. I plan to measure mine once the Currie/Savvy 4" is installed so I will definitely share that.
 
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jjvw said:
Those models are from the 4 link calculator. Some time should be spent discussing it. The calculator is flawed in that it only shows these forces on flat ground. In reality, the instant center changes with the suspension travel. The antisquat line also shifts as the suspension travels and as the vehicle tips, rolls and moves around. Because it is partly determined by the center of gravity, the antisquat line even changes with added cargo, passengers or an empty tank of gas. What actually happens on the road and on the trail is quite a bit different from what is shown in the calculator. We do run the risk of fixating too much on the lengths and measurements we see on the screen rather than trying to understand the overall concepts.

What is important (and where this matters for the vast majority of us) is to understand that these forces exist, they have real world implications on our modified Jeeps, and that they can be manipulated if you have the resources and know what to do. Most of us do not have the resources or know-how to build and refine our own custom suspension, so we must rely on kits. What sets the Savvy kit apart from all other "longer arm" kits is that it was specially designed with these suspension dynamics in mind.



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I went back and added some clarification for why we should not pay too much attention to the 4 Link Calculator beyond understanding the concepts behind it.
 
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CasperLLY said:
Wow! Lot of good information for a newbie

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Trust me, I'm still trying to understand all of this. There are so many moving and shifting variables, that it can become difficult to see what is actually happening. This is especially true when you take a step back and look at the entire vehicle as a whole.
 
You need a solid understanding of physics to really grasp the whole concept of a suspension designed to do what we force it to lol.


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I've been reading about and discussing this topic a bit the last few days and thought I would add a few more things.

Earlier it was duscussed that the true purpose of longer arms is to correct the positioning of the instant center by moving the control arm mounts because lifted short arms place this point too high. An interesting observation of the Rough County long arms was pointed out to me. This kit may be an example of the instant center being pointed too low, resulting in too little antisquat (too much squat, to rephrase).

The observation is that during a steep climb, the loading of the rear suspension pulls the back end down to point that the front end unloads and the Jeep will want to flip backwards!

The assertion would be that the corrected geometry has gone too far in the other direction as compared to lifted short arms.
 
I havent run numbers yet, but to improve my instant center it seems I would benefit from moving my mounts. Ive seen on other forums (JF) where people have re-drilled the frame side lower control arm mounts in the rear. Im assuming the same can be done for the front on both lower and upper mounts. The problem I see in my head is the new upper relocated mounts would limit uptravel as the frame would now be the interference point? (thinking on short arms)
 
tworley said:
I havent run numbers yet, but to improve my instant center it seems I would benefit from moving my mounts. Ive seen on other forums (JF) where people have re-drilled the frame side lower control arm mounts in the rear. Im assuming the same can be done for the front on both lower and upper mounts. The problem I see in my head is the new upper relocated mounts would limit uptravel as the frame would now be the interference point? (thinking on short arms)
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The old Nth Degree short arm kits came with a jig for drilling and lowering the lower control arms. It is certainly something that can be eyeballed. I don't recall if anything was done to the uppers.

I imagine there would be some benefit to the geometry, but at the expense of clearance at the lower arm. It may not be physically possible, but the vertical separation at the frame should not exceed the separation at the axle.

It would be interesting to know why drilling the mounts never caught on outside the Nth kit.
 
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