EDIT: I guess that I'd best title this as my collection of thought on the topic. It is by no means complete, but I've hit the high spots.
My thinking is that traditional trailer springs are short and stiff to keep the ride height nearly unaffected by the loading and to eliminate the need for damping. That makes things simple and easy to design and to install.
It also results in broken parts if not just broken eggs when used on rough roads or off road.
There are some roll-steer characteristics of leaf springs with live axles that need paying attention to, but largely that is a function of the spring hangers and can be dealt with by buying all of the parts as a package.
Adding a damper to those short and stiff springs will help, but the basic problem is the springs being stiff. The Torflex axles are one potential solution to the rough ride of the short & stiff leaf springs. Reportedly those have issues with long distances on washboard roads. The failure mode is for the trailing arm to work it's way out of the mounting tube. That would be pretty hard to fix in the field. My TrailBlazer has this type of axle under it. It also has significant mileage on Baja's washboards, and a trip to Copper Canyon under it's belt (before my custodianship of the trailer). It has not had a failure of this (or any) type. The sole difference that I can see is that the man who built it's substantial replacement frame added dampers in the form of Rancho RS9000's. I'm not all that fond of Rancho shocks, but I see no reason to change something that is working.
My theory from afar is that washboard roads work this type of suspension hard and fast enough to generate some significant heat in the rubber. I suspect that this heat is great enough to break the vulcanizing bond, which allows the trailing arm to work it's way out of the mount tube. AFAIK this bond is all that holds the trailing arms in place. It must be pretty significant to not be a liability concern to the mfg. I have pondered adding a strap across the end of the trailing arm that would prohibit it from walking out should the de-vulcanization come to pass.
The problem with soft spring rates is that they vary ride height with loading. I only see two potential problems with this, cosmetics of the trailer following the tow rig, and the potential for the tire to rub on the fenders. The third potential problem, flopping over, to me is indicative of too soft of a spring rate.
This ride height vs. loading variance is what lead AT to use an air spring. With an air spring the ride height is easily adjusted. I think that they missed the boat in one option though. There are off the shelf electric & pneumatic switches that could make the trailer self-leveling, and then allow that feature to be turned off when desired or necessary.
Trailer suspension need only deal with bumps and not with articulation. Ever notice how easy it is for one leg of a 4 legged stool to be off by just enough that the stool wobbles? Doesn't take much. Three legged stools never have this problem. Articulation deals with that 4th point not being on the same plane as the other three points, but still allows for stability. Trailers only have the three points ( the toggle link between tandem tiress acts as an 'averager'), two tires and the coupler. They never wobble like a four legged stool with a short leg or like a tow rig with one tire in the air.
The advantage of "ITS" (Independent Trailer Suspension) over a live axle is the same thing that lead to independent use on passenger cars, one tire's bump does not influence the other tire. This is a ride quality bonus. I don't see going to the trouble of linkage and springs other than leaves, but keeping a live axle as being worth all of the trouble. For a one-off ITS build I would use a live axle and build the trailing arms to it. Once everything was built and finalized I would then cut the middle out of the axle tube itself and cap it. There need not be any fancy linkage geometry. Arguably there may be some small advantage in using some fancy geometry, but my estimate is that you're now talking about out there in the extreme 2% region. A simple single pivot axis trailing arm will do the job. Biggest concern is designing the trailing arm such that it can take the hard hits to the tire. There is a fair amount of leverage involved, the arm itself will need to be fairly rigid in design.
For those considering the Lock-n-Roll there is now a U.S. alternative called the "Max Coupler."
http://www.adventuretrailers.com/coupler.html
An OZ option is the "Treg Hitch", but I know of no vendor in the US. Of the three I like it the best, mostly for it's urethane block that acts to absorb any impacts that the trailer might try to transmit to the tow rig.
by Gerdo » Fri Sep 15, 2006 5:44 pm 
seems to be what I've gotten so far...
Wright
What I was seriously wondering was the most of the Off Road trailers I've seen are steel/aluminum, and reinforced, with putting a tear on a frame made for trails and rocky terrain, (and the inevitable evil that is washboard) aren't we taking a chance on dislodging or just down right bustin somethin, with a hard hit, or vibrations. With putting an (somewhat) articulated suspension underneath, will it be an appreciable reduction in the chance of that happening. I know that low and slow driving with the trailer is the best bet, but as Y'all know, mistakes happen, and washboard will wear down just about anything...
I've drawn about a dozen pic's and still cant wrap my mind around it... Unless its a bolt-on sort of Quazi-roll cage that wraps the tear body... still thinking on it....
