Radius Arm Suspension

[worthingtontw]

After I wrap up my current truck project I'm thinking about building a gear trailer. I have some FZJ80 radius arms left over from an abandoned project and I'm thinking they would be good to re-purpose for this application in a trailing arm arrangement. I'm thinking that it would allow for more up travel than a 3 link, while also eliminating axle wrap during braking with leaf packs. Only real down side I see is the inherent reduced flex left and right, but I figure roll would be compensated for at the receiver.

Shooting for 800-900lbs empty. Box steel frame, with fiberglass body similar cosmetically to an XVenture.

Thoughts or concerns?

 

[worthingtontw]

No one has any thoughts on a radius arm suspension? I think biggest benefit is you can have the frame closer to the frame than a leaf setup yielding a lower deck height while maintaining up travel. Not as fancy as an independent trailing arm setup but I imagine as effective as anything else. Only issue I see is alignment but provisions can be made.

 

[croix]

I don't see any reason that a radius arm suspension wouldn't work. You've identified the issue with side-to-side flex. The only other I see is the axle rotation with up/down travel which "could" create some spring alignment issue in extreme travel. With a generally neutral suspension (up-travel = down-travel) overall deflections should be minimal depending on the length of your arms. I went through a bunch of crazy math on my suspension only to find out that deflections were about 1/2" with 20" control arms. That means that with one side fully compressed and the other side fully extended I could theoretically see a 1" difference from one side to the other. In reality, I've never been close to that situation and as you pointed out, the roll is compensated for at the receiver (especially with a max coupler or L-N-R).
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Unless you are using really soft springs and are designing a suspension that will travel more than 6" then I think radius arms are a good fit for the same reasons you stated. Good luck.
-croix

 

[richxd87]

Does anybody else have any thoughts on this? I arrived at the same idea to use 80 series radius arms and a panhard but with air bags and shocks. I think this will be easier to implement than an independent trailing arm design. My main goal is to use airbags so that I can adjust my spring rate to my load and have a smoother ride for the trailer.

80 series radius arms shown below

 

[cjmoon]

Does anybody else have any thoughts on this? I arrived at the same idea to use 80 series radius arms and a panhard but with air bags and shocks. I think this will be easier to implement than an independent trailing arm design. My main goal is to use airbags so that I can adjust my spring rate to my load and have a smoother ride for the trailer.

80 series radius arms shown below

Obvious draw back to air bag is in lose of air. I have the intention of adding air bags to my leaf spring trailer for heavy loads. I have a 4 inch drop axle with spring under on long truck leaf springs and shocks. Used a slider style shackle and have a ton of clearance. A pretty low cost set up. Use a Jeep Wrangler rear coil with air lift bags inside that way you have a base load mechanically taken care of then extra with air


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[ottsville]

Why is this better than under-springing your trailer and adding air bags?

 

[richxd87]

Why is this better than under-springing your trailer and adding air bags?

I think...

With the leaf springs, I'd still be contending with the additional spring rate and load capacity of the leaf pack.

If I ran airbags on a single leaf to minimize it's load sharing, I think it would fatigue the leaf at the localized point, potentially causing premature failure.

The leaf springs wouldn't react/cycle as quickly to variations in the road compared to an airbag as the primary lift spring.

These are just some of my assumptions, be glad to discuss or hear other thoughts.

Richard

 

[ottsville]

Thanks for the reply, I was curious as to the thought behind it. I tend to think along the lines if "what will be the easiest to repair/find parts for if 'x' breaks?" Leaf spring systems are so common that parts can be found almost anywhere.

If I ran airbags on a single leaf to minimize it's load sharing, I think it would fatigue the leaf at the localized point, potentially causing premature failure.

I was visualizing an airbag directly over the axle, with a light spring being mainly used for axle location. Again, springs are easy to find and replace if broken while travelling. (edit: and a broken airbag while travelling could be resolved by temporarily installing a complete spring)

The only problem I see with regards to radius arms is that in this situation is the axle sleeve becomes a torsion bar with potential fatigue issues.

Sounds interesting. I'd like to see how it works out.

 

[CampStewart]

It looks to me like you will be loosing several inches of clearance under the axle which in reality may be more important in theory than in practice. I have a feeling that by the time you are done you would have been better off building your own radius arms shaped to your needs. I like the single long leaf with airbag and panhard idea better though axle wrap under braking as previously mentioned might be an issue with it.

 

[LandCruiserPhil]

Keep it simple trailer suspension travel is over rated and not needed.
AT tried the air bag suspension and it was a huge failure, just say'n

 

[honda250xtitan]

Do it, the "cool" factor alone is worth it. Half the reason for these trailers is to tinker with them.

 

[cjmoon]

I installed the overloads to the top. Not ideal but needed them for an abnormal use. 3 dirt bikes and gear for 4 guys camping. Typically I’m not loaded down that heavy. Tons of clearance.

On a side note. mount that radius arm to the top of the axle upside down like some of the big lift 80’s do.


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