Radius arm vs True long arm

YJJPWrangler87

YJJPWrangler87

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Joined
Mar 12, 2006
Location
Raleigh
Building a longarm kit for a XJ for the front. Whats better, the radius design or the true longarms. I've only seen RE and Rustys and I know that those are the radius designs. Which is better for offroad or highway? I've heard that the radius style is for better droop. this XJ is mostly offroad but it will be driven onroad to. Still early in the fab phase so I can change pretty much anything. Any ideas?

Zack
 
Assuming they're both built and designed correctly, multi-link suspensions are better than a radius arm in all aspects excluding simplicity.

But, Radius arms are harder to screw up the geometry on by far...
 
yeah thats what i figured..i also heard that a 3-link like the rockcrawlers suspension is also easy to do and build.

Zack
 
Thing about a 3 link, as I understand it, you can get your roll center alot lower a hole lot easier than a double tri, 4 link on most vehicles.
 
well heres the situation.. my gf bought a 92 XJ as a toy...not really for onroad more offroad. Its gonna be a budget build cuz shes a college student and so am I. but I also don't want to do anything to extreme just yet since shes only been wheeling(as a driver) a couple of times...buts shes impressed the hell out of me driving so its all good. we already have 4.5 RE coils along with Rustys 6.5 leafs...gonna do longarms, got the RE joints, and gettingg teh DOM this saturday. Should I do radius or longarms...any opinions? I know there has to be at least a couple of ppl on here that have made their own control arms.

Edited for csudman: so would a tri-link be better than radius/long arms??

Zack
 
For the front of an xj. Radius arm is the easiest way to go. Beyond that, if your running a triangulated 4 link front, you really need to go full hydro. And I dont think it will fit without pushing your front axle forward a long ways.

The other thing is if you do a 3 link, you can use the existing mounts on your axle to attach everything to. This is obviously not a trail only rig so I dont think your gonna wanna screw with all that work especialy with a dana 30 front.

As far as design, I honestly like the way rockkrawlers newer system attaches.
Its pretty straight forward and allows for alot of travel.
 
yeah i am gonna agree with csudman on the rock krawler independent three link, which i told you earlier today would be the easiest build and provide the best flex.
 
i thought that the rockcrawlers setup, the upper link had a fixed point on top of the diff. or am i wrong?

Zack
 
well, fixed is relative. Their is a bushing on the top of the dif, So you will have some deflection there. I had the RK Xfactor or whatever they call it now lift on my old cherokee. It had a rebuildable peice of crap joint in its place. I'd jsut run the bushing. Simple and cheap, oh and it was a huge bitch trying to get that old bushing out of there, your better off to use whats there.
 
alright....so i can still use the orignal LCAs right? and would i have to fab something over the diff...im lookin on RKs website and for the singler upper...theres one bushing and then theres a bracket..where does thta bracket attach to? im pretty sure im gonna have to make a crossmember...is that where the bracket attachs? used to leaf springs:shaking: so im still learning my way around coils and stuff.

Zack
 
This is about how it should look, in simple paint.

P.S. I think these colors look great too.:flipoff2:

untitled.jpg
 
alright....so i can still use the orignal LCAs right?

You can use the origanal mounts on the axle, although I would at least weld some steel across the bottoms to stiffen them up and act as a skid

and would i have to fab something over the diff...im lookin on RKs website and for the singler upper...theres one bushing and then theres a bracket..where does thta bracket attach to?

No, you simply use the factory upper mount on the axle.

The Bracket goes inside the frame rail, you will have to fab a braket for mounting the upper arm, as you will with the rest of them anyway.

im pretty sure im gonna have to make a crossmember...is that where the bracket attachs?

You dont have to make a crossmember, the rk mounting system worked ok, I would just see if you can buy it from them seperatly. Probably save you a ton of time.
 
sweet....explains to me perfectly, and the gf will love the pink...so no crossmember just a special bracket. on RKs website...which bracket is it?

Zack
 
On a related not but different vehicle, does the upper long arm on the driver side need to be on top of the diff for the setup to work well? Can the two long arms on the driver side be vertically above and below the other?
 
hmm...what vehicle is it on? im assuming that if the driver side UCA and the driver side LCA were on top of each other, that it would limit flex...but thats just me.

Zack
 
YJJPWrangler87 said:
hmm...what vehicle is it on? im assuming that if the driver side UCA and the driver side LCA were on top of each other, that it would limit flex...but thats just me.
Click to expand...

Naaah. as long as they don't hit.. but see below...

csudman said:
It would work fine. just realize that you will need a track bar with the 3 link.
Click to expand...

And if you decide to make it a 3-link.. make that single upper STRONG, to include the joints, mounts, etc.. it's gonna see a shit-ton of force. (another reason to try and squeeze that 4th link in there).

But, if you can't triangulate the upper link in eough to control side-to-side movement, then run the trac (panhard) bar, and DON'T triangulate that upper link at all.. it'll cause binding as the 2 fight each other..

(Can't find the thread where the guy found that out the hard way, but fortunately, still during the mock-up phase)

edit: This doesn't deal at all with steering, which is another reason to run a trac bar if you're not running full hydro.. damn near a requirement. I keep forgetting to mention it, since my next setup will be full hydro.
 
Oh definitely. I planned on running the trac bar no matter what. So dont offset the side with upper and lower long arms at all? Can they be slightly offset, or if I'm going to run a trac bar should I just run them vertically aligned?

I'm not to sure on the 4-link setup, with the geometry and all, so unless I get a crash course and formulate a setup on paper, I probably wont run it.

I'll try to post a basic design picture of what I'm planning on running here soon, unless I go with radius arms for the time being :shaking:
 
ok so for the 3-link design for a XJ, i would have to run a trackbar to keep the axle from moving side to side right? and if i do run the trackbar, I don't have to triangulate the upper control arm and vice versa right? can anyone give me a pic on paint or something like that?

Zack
 
a.) what are you gonna do when that upper link breaks?
b.) why not make something similar to RE/Clayon longarms with 2 radius arms coming off of the lower longarm? This way you don't have to make some mount for the upper.

Theres no sense in reinventing the wheel, most LA kits on the market for base vehicles are well engineered and designed. Now just rip off their design. :D
 
You may want to examine a few 3 links on rigs that you've seen WORK.. There's every bit as much design as a 4-link, and if you do it wrong, it'll drive worse than a radius arm-based design. Not trying to discourage you, just making sure you're sure of what you want to build before you put steel to steel..
 
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