Control arm length

[Art Welch]

My jeep has been out of service and in need of some serious attention for a long time now and I'm finally going to get on it. One of the many things it needs is a suspension redesign and rebuild.

At present it has what I believe are approximately stock length TJ arms (16 inches bolt to bolt on the front lowers) with 38s. As you can imagine the arm angles aren't good. To compound things the tires I'll be running after the rebuild are a couple of inches bigger.

I can add about 6-7 inches to the arms easily enough as part of pushing the axles forward and back without doing much relocation of the frame end lower control arm mounting points. But in your experience would 23 inch lowers be smaller than what you would want to run with 39-40 inch tires? My guess is yes but going longer than that will mean either some very creative mounting or moving the frameside mounts back far enough that I will give up an uncomfortable amount of clearance.

Once I sort out the target length for the lowers I'll do the math on the uppers and relative angles but the lower length feels like the best place to start.

[Robert J. Yates]

I'd actually start with the math first before I tried to arrive at an arbitrary length. This thread is pretty interesting and helpful.....

http://www.pirate4x4.com/forum/showt...ink+calculator

[chef]

No it's not, it's incredibly frustrating. You can read a hundred different opinions in that thread and play with the calculator quite literally for hours.

I haven't gotten to test my front yet, but I built it to have near 8" of seperation between the upper and lower links and be parallel. I stuffed the mounts where ever the hell I could. Links ended up being a hair shy of the length of my rear links, which isn't a big deal because of the threaded Johnny Joints on one end. I have no clue what the anti-dive is or how any of it will react. Hopefully "nice" The caster change is minimal due to the near parallel arms. From what I've read, I should have placed the upper on the passenger side to combat torque lean, but it would have meant even more rearranging of previously mounted goods then I was already facing. I'll see how it turns out and then decide what adjustments are necessary.

The rear came out really well. I wish I could remember the length off the top of my head, I think 34.5". The uppers are 5" apart at center at the axle, and mount right at the frame, 40" wide? Something like that. I mounted the lowers as far out as possible on the axle, about 2-3" above axle centerline, and offset the other end at the frame one joints width inside of that. They mount about 2" below the bottom of the frame. This worked out incredibly well. According to the calculator it provides a fairly flat roll axis (keeps the axle drooping straight down rather then on a large arc, commonly referred to as flex steer), an anti squat value of around 80%, and the instant center (the point that the suspension rotates the vehicle upon and some other stuff that's very confusing) is out in front of the bumper. There's 8" in between the uppers and lowers at the axle, and 6" at the frame...Everything ended up the same as what Mike Shaffer suggested, except he likes the links a little longer. No matter because it works great.

That's my story. The front is based off some tips from Blaine, the rear from tips from Blaine and Matt Pascoe and Mike Shaffer.


To really flip your lid and make things even more complicated, take a look at a moonbuggy or a pro mod car and try to figure out how the hell the link setups work so well on those.

[Robert J. Yates]

Your answer that is confusing to me....you suggest that you used the calculator to confirm your link layout to good result yet your first words are that the thread is frustrating. I agree that the thread is confusing but the calculator is there for the taking (its in the guys signature line) and I guess thats the part of it I was presenting.

Its ok to start with a number but the math is the math. Once you have that, then you can decide how you want to compromise base don your rig and how much work you want to do but then as I said in my original reply......that would be if it were me.

[Matt Pascoe]

Originally posted by Robert J. Yates
Your answer that is confusing to me....

Clearly Robert hasnt played with custom links yet

The threads are very confusing and often contridict logic. The calc will tell you the numbers for your design, but not weather or not it will work well. Winds up being a very time consuming compromise.

Adam, your right, watching the moon buggies suspension work blows my mind.

I think I wound up with around 34" for my rear links. It works, but I'm sure could be better.