Need Help With Lower Control Arm Sizing

C

Cody Brought

New Member
Joined
Apr 4, 2024
Messages
19
Location
Selinsgrove PA
I am getting started building a custom long arm suspension for my 98 wrangler. I am building axle trusses for my dana 30 and 44 and want to extend the frame side mounts as close to the transmission crossmember as i can for better angles since I have a 4" lift. But since I'm slightly less than doubling the length of the arms, the forces are going to be greater.

Does anyone have experience with building custom control arms? If so, what size and thickness pipe should I use for my uppers and lowers?

I am using enduro joints and welding threaded tube inserts to steel DOM tube

All brackets are 1/4" thick

I'm building the jeep mainly for cruising offroad and doing small jumps, not much rock crawling is planned at all

Rear upper links will be triangulated

Running 33's, plan to get 35's later

I plan to use 1.5" OD tube with a .120" wall for my upper arms, and 2" OD tube with a .25" wall for my lowers; the thicker wall is for more resistance to denting.
My main concern is the diameter of my lower control arms. Is 2" strong enough for a longer arm? I'd rather go with 2.5", but I cant find threaded inserts that fit a 2" internal diameter.

Id appreciate any feedback, as even though I'm well educated in material science I have no experience applying it and can't find much information on this.

FYI this is my DD and I have cast outer knuckles, so i will not be doing any impressive jumps, mostly high speed cruising offroad and hitting bumps
 
Most on there would consider the long arm as not a good option, build a mid arm and be good to 40’s. Good luck
 
astjp2 said:
Most on there would consider the long arm as not a good option, build a mid arm and be good to 40’s. Good luck
Click to expand...

Help the guy out and explain that it isn't even the arm length that matters. The positioning of the control arm mounts create the suspension geometry. He should focus on that. The arm length is just the length need to connect point A to point B.
 
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2 inch 0.25 DOM will be plenty strong for the lowers, even if you are bashing it in the rocks.
 
Cody Brought said:
I am getting started building a custom long arm suspension for my 98 wrangler. I am building axle trusses for my dana 30 and 44 and want to extend the frame side mounts as close to the transmission crossmember as i can for better angles since I have a 4" lift. But since I'm slightly less than doubling the length of the arms, the forces are going to be greater.

Does anyone have experience with building custom control arms? If so, what size and thickness pipe should I use for my uppers and lowers?

I am using enduro joints and welding threaded tube inserts to steel DOM tube

All brackets are 1/4" thick

I'm building the jeep mainly for cruising offroad and doing small jumps, not much rock crawling is planned at all

Rear upper links will be triangulated

Running 33's, plan to get 35's later

I plan to use 1.5" OD tube with a .120" wall for my upper arms, and 2" OD tube with a .25" wall for my lowers; the thicker wall is for more resistance to denting.
My main concern is the diameter of my lower control arms. Is 2" strong enough for a longer arm? I'd rather go with 2.5", but I cant find threaded inserts that fit a 2" internal diameter.

Id appreciate any feedback, as even though I'm well educated in material science I have no experience applying it and can't find much information on this.

FYI this is my DD and I have cast outer knuckles, so i will not be doing any impressive jumps, mostly high speed cruising offroad and hitting bumps
Click to expand...

High speed off-road? 🤨
 
jjvw said:
Help the guy out and explain that it isn't even the arm length that matters. The positioning of the control arm mounts create the suspension geometry. He should focus on that. The arm length is just the length need to connect point A to point B.
Click to expand...

I want to make the arms longer so the angle of the arms is reduced. Is there a generally acceptable control arm angle i should shoot for? I'm going to move my upper mounts about an inch higher to get my uppers mostly straight, and i want them to be about 85% of the length of my lowers.

If id move my lower mounts up that would put my axle mounts closer together, so wouldn't they have less leverage and be prone to breaking off the axle? I appreciate your thoughts
 
JMT said:
High speed off-road? 🤨
Click to expand...

Yeah, "high speed". I drove on a construction site once and enjoyed cruising about 40-50 on the dirt roads, but i had to watch bumps a lot because i didn't want to ragdoll my front axle or control arms. I dont know what is considered high speed in the offroad world, I'm really a beginner. Id appreciate any advice if you had it.
 
Cody Brought said:
Yeah, "high speed". I drove on a construction site once and enjoyed cruising about 40-50 on the dirt roads, but i had to watch bumps a lot because i didn't want to ragdoll my front axle or control arms. I dont know what is considered high speed in the offroad world, I'm really a beginner. Id appreciate any advice if you had it.
Click to expand...

You are being distracted by control arms when you really ought to be looking at shocks.
 
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kmas0n said:
2 inch 0.25 DOM will be plenty strong for the lowers, even if you are bashing it in the rocks
Click to expand...

Thank you, I figured as much but I'm new to this stuff so an experienced opinion is nice to have.

The stock upper arms were smaller than the lowers so I figured 1.5" DOM was strong enough, and a .120 wall was good because no rocks would hit it.
Is that assumption correct? I could go with the same size as my lowers but metal and joints are expensive and I'm trying to save where I can.
 
Cody Brought said:
Thank you, I figured as much but I'm new to this stuff so an experienced opinion is nice to have.

The stock upper arms were smaller than the lowers so I figured 1.5" DOM was strong enough, and a .120 wall was good because no rocks would hit it.
Is that assumption correct? I could go with the same size as my lowers but metal and joints are expensive and I'm trying to save where I can.
Click to expand...

.120 dom for the uppers will be plenty too. The uppers only receive compression/tension forces, no side to side load.
 
For the rear shoot for lower arms at 26-27 inch in length. Keep the axle side mount in the stock location. For the upper try for as much separation at the axle and frame as packaging allows. Hopefully you are running body lift or you will be short changing yourself in tha ability to get ideal separation.
 
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Blackjack said:
For the rear shoot for lower arms at 26-27 inch in length. Keep the axle side mount in the stock location. For the upper try for as much separation at the axle and frame as packaging allows. Hopefully you are running body lift or you will be short changing yourself in tha ability to get ideal separation.
Click to expand...

I dont have any body lift, only a 4” spring lift. How does the body lift help with my link separation?
 
Cody Brought said:
How do the shocks play into my vehicles strength? And what type of shocks should I get that would fix my issue?
Click to expand...

You are making an assumption that there is a problem with strength that needs to be addressed.

Shocks are a significant part what allows the vehicle to maintain to maintain control and stability. Longer arms are not doing what you think they do.
 
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Cody Brought said:
I dont have any body lift, only a 4” spring lift. How does the body lift help with my link separation?
Click to expand...

By creating room above the frame to position the upper link mounts, both frame and axle.

An alternative is to chop open the tub.
 
jjvw said:
You are making an assumption that there is a problem with strength that needs to be addressed.

Shocks are a significant part what allows the vehicle to maintain to maintain control and stability. Longer arms are not doing what you think they do.
Click to expand...
The reason i want longer arms is so my axles arc along its travel is reduced, and the lower angle puts less force on the axle and frame and directs it towards the spring. I got new shocks recently and it helped with my stability, now im trying to make it easier for the jeep to flex and make the axle assembly stronger.

Thats what I think the longer arms will do, please let me know where I’m misguided. I appreciate it.
 
jjvw said:
By creating room above the frame to position the upper link mounts, both frame and axle.

An alternative is to chop open the tub.
Click to expand...

Im hoping my upper links dont go any higher than where the raised trackbar mount is, but that will be cut off. Ill set my bumpstops accordingly and might get a body lift later at 1” or so. Thank you
 
Cody Brought said:
The reason i want longer arms is so my axles arc along its travel is reduced, and the lower angle puts less force on the axle and frame and directs it towards the spring. I got new shocks recently and it helped with my stability, now im trying to make it easier for the jeep to flex and make the axle assembly stronger.

Thats what I think the longer arms will do, please let me know where I’m misguided. I appreciate it.
Click to expand...

Your assumption is founded, but if you do some research with real knowledgeable people not trying to sell you something it may change your mind. Control of the vehicle cannot be fixed by control arm length, shocks are 90% of the ride quality and road handling stock geometry is adequate for 80% of most drivers. Those others who need that extra can get by with a midarms. Do some searching on here and you can see the discussions and make your decisions for your build. Good luck 🍀
 
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