Short-Long Arm/Equal Length Arm Suspension design

[ntsqd]

I can't quite tell if these are Short and Long A-arms, or Equal Length A-Arms, but I wanted to preserve these pictures for future reference as they were part of a CraigsList ad. The topic of building arms this way pops up from time to time and I thought some pictures might come in handy.

 

[ersatzknarf]

Looks somewhat like an ATV rear suspension ? I think I can see an outboard drive flange coupling in one of the shots...

 

[Outback]

I like this design for a Jeep. Matches real nice.

 

[R_Lefebvre]

Guess I missed this the first time. Looks equal length to me. Or at least pretty close to it.

I see the drive flange too.

I still think independent suspension on a trailer isn't really necessary.

 

[indiedog]

I still think independent suspension on a trailer isn't really necessary.

I think it depends on how robust your trailer body and its contents are and where you intend to take it. I'm looking at using composite panels with little or no framing for my next build and I have no doubt that independent suspension will be "kinder" to the body. Check out the Track Trailer vid. Pretty amazing viewing. [ame="http://www.youtube.com/watch?v=oa4BgNF8eKQ"]Track Trailer[/ame]

 

[Eric06Rubi]

it does look like an oversize rear suspension from some kind of atv. can someone with a mule verify?...interesting idea tho.

 

[ntsqd]

I don't know that I'd put a lot of effort into finding ATV parts. Unless the trailer is tiny and/or the loading is really light, you're likely to be pushing on their design limits pretty easily.

OTOH there are a lot of compact car options out there. The Locost 7 building community uses McPherson strut uprights in SLA suspensions by cutting off the strut tube and welding in a threaded plug for a spherical rod end. The control arms can be made nearly identical with a simple plywood fixture.

 

[Tight_wad]

I think it depends on how robust your trailer body and its contents are and where you intend to take it. I'm looking at using composite panels with little or no framing for my next build and I have no doubt that independent suspension will be "kinder" to the body. Check out the Track Trailer vid. Pretty amazing viewing.

I would like to see this on a track that has staggered left and right humps. I would be surprised if it does much different then a solid axle trailer. Independent suspensions work best when you have 4 contact points.

 

[RR1]

it does look like an oversize rear suspension from some kind of atv. can someone with a mule verify?...interesting idea tho.

it is definitely off a ATV or Side by Side, you can see the U-Joint on the inner hub.

Thought IFS was a big no-no for rock crawlin'. :ylsmoke:

 

[seanz0rz]

in the picture above, if the suspension was properly set up for the vehicle, the tire on the rock should be compressing, but it is not. (yeah i know the trailer isnt loaded, so maybe it does this when it is)

its a very creative idea, but without easily adjustable suspension to compensate for changes in load (airbags work GREAT for this), the suspension just doesnt work like it should. id say this was fairly well executed though. equal length arms should give that thing a decent contact patch for what it was designed to do.

my 3/4 ton springs on my M762 are so stiff, i get no articulation out of them. i might end up removing a leaf or two to make them a little more pliable and suited to my needs.

 

[R_Lefebvre]

I think it depends on how robust your trailer body and its contents are and where you intend to take it. I'm looking at using composite panels with little or no framing for my next build and I have no doubt that independent suspension will be "kinder" to the body. Check out the Track Trailer vid. Pretty amazing viewing.

The difference between the truck and trailer in that video is not because of the difference between independent and solid beam axle suspension. Well... it is in a way, but not for the reason you think.

The difference you are seeing is because the trailer's suspension has a much lower unsprung mass. Not because the trailer's suspension is independent. The independent suspension has a lower unsprung mass.

I also fail to see the point in putting a more sophisticated suspension on the trailer than what is on the tow vehicle. So the trailer is capable of a speed which the tow vehicle is nearly uncontrollable. Slow down, before you crash.

A couple other points:

1) An independent suspension with 35" tires has huge unsprung mass, and you loose that benefit anyway.

2) a trailer live axle will have less unsprung mass than a truck axle anyway, since there is no driveline inside.

Sean touched on the other reason why I think independent suspensions are not necessary. A trailer is a tripod. No matter WHAT you do, independent suspension with airbags, etc... the trailer is a tripod and it will always tilt when one side goes over an obstacle. Articulation is meaningless. That trailer could have air bags, linked airbags, springs from a Nissan Micra, it doesn't matter. It will tip.

At speed, you can get some independent action, however. The inertia of the trailer stops it from tilting, so you need to be able to absorb bumps on one side. However, solid axles can and do absorb bumps on one side. The only negative aspect, is that the other side experiences a camber change when one wheel hits a bump.

That's bad for a sports car. I don't see why a trailer would care. If it really makes a difference, you're probably cornering way too fast on a bumpy road, and as the video demonstates, the truck probably already lost control as well.

 

[RR1]

I don't see why a trailer would care. If it really makes a difference, you're probably cornering way too fast on a bumpy road, and as the video demonstates, the truck probably already lost control as well.

I wouldn't do it for going fast per se, I would want to have independent suspension on a trailer so the the gear on the trailer doesn't get beat to Hell.

I am converting my single axle moto trailer to trailing arm for such reason. I threw my mountain bikes on with my dirt bikes (to get 'em off the roof of the truck for better mpg's), big mistake the mountain bikes got beat to Hell going down washboard roads, even though they were in a tray. The vibration had blown the fork seals by the time I got to camp, plus a bunch of hardware came loose.


Of course I have a full tilt boogy suspension on my adventure rig...it will go fast off road. Pulling nearly 20" of travel front and rear.:smiley_drive:

 

[Tight_wad]

in the picture above, if the suspension was properly set up for the vehicle, the tire on the rock should be compressing, but it is not. (yeah i know the trailer isnt loaded, so maybe it does this when it is)

But since it is a trailer, and the only other contact point is the hitch, it just can't really compress like that. The only real way to have it compress like a vehicle, is if it had a self leveling system on it that would raise and lower each side to keep the trailer itself level. I think that this would be more complicated than an of these trailers really need.

 

[jesusgatos]

I would like to see this on a track that has staggered left and right humps. I would be surprised if it does much different then a solid axle trailer. Independent suspensions work best when you have 4 contact points.

Only real potential advantage I can see is ground clearance and packaging.

 

[Tight_wad]

Only real potential advantage I can see is ground clearance and packaging.

That is the best reason that I have heard to support the I.S. But then again, there are ways to create more ground clearance with a solid axle too.