hit the nail on the head there.
Well, if I reeeeeeally had my heart set on independent suspension for the rear, I'd look for something off of the rear end of an old VW. Longish trailing arm, off the shelf parts and it's hard to argue that a design that's been in use since before WWII isn't reliable. It wouldn't take much effort to make it work. The downside is that it's going to take effort to make it work. You'll have to source a donor and figure out how to make it work. If you have the resources and abilities to make the VW trailing arm work, you've likely got the resources and abilities to build your own trailing swing arm from scratch.So here's some of my thoughts.
Proper IS using long-arm trailing arms are best obviously, but pre-built assemblies for bolting in to a trailer are pricey. An order of magnitude kind of pricey.
Common trailer dead-axles perform worst off road. A solid axle is great for a driven-axle but seems prone to jounce and trailers seem to bounce around like crazy.
Torsion axles that use rubber have been failure-prone in the past. I cannot speak to existing products but Andrew White talked about an expedition trailer that failed on him in the middle of nowhere when a torsion axle gave out.
Likewise, newer rubber-block-suspended trailing arms seem more oriented towards low deck height instead of long travel or high ground clearance, and I have my long term concerns about the longevity of the rubber blocks.
The Nissan F-Alpha platform suspension is meant for vehicles intended to go well over 100,000 miles. It may not offer the travel of the heavy duty, purpose-built long arm suspensions, but looks like a good compromise of ground clearance, long term durability, cost, and field serviceability. It also looks alignable in a regular alignment shop and should remain well aligned as it articulates on pavement, as it had to in its original application on a passenger vehicle. Furthermore those trucks had 7000lb towing capacities on top of the original vehicle weight. It might be more an issue trying to find soft enough springs if the trailer weighs less than the original axle load had in the SUV.
********, yeah nothing at all wrong with torsion axles. Anyone who says otherwise is on something, or had a defective part that should have been warrantied.
The motion ratio on this shock is bordering on useless.
How so?The motion ratio on this shock is bordering on useless.
Pretty sure those are torsion Bars. The torsion axle in a trailer uses a big chunk of rubber as a spring and damper in one.My 1975 Volkswagen Westfalia would disagree with this sentiment.. 45 years in service and its rear torsion axle is riding just like it always has.
The axle moves in an arc. It really doesn't move back all that much compared to it's vertical movement. As the axle goes up the shock leans over more giving it a decreasing ratio or falling rate. If you cycled that set-up you would see that at full bump the shock would be doing almost nothing. Exactly what you don't want.How so?
It almost directly opposes the travel that the axle sees as the suspension compresses. Leaf springs cause the axle to move aft as well as up when the suspension compresses.
Is it ideal? In a perfect world it would be mounted more vertical. In the real world that would require a stupid amount of lift, mounting to the axle so that it hangs down much lower or cutting a hole into the cabin of the teardrop.
It's not a racing teardrop and my experience of actually towing the thing with and without shocks shows me that they're working.
When the axle moves up three inches it also moves back almost two inches. The picture shows it unsuspended, it compresses almost an inch with the weight of the trailer on it.The axle moves in an arc. It really doesn't move back all that much compared to it's vertical movement. As the axle goes up the shock leans over more giving it a decreasing ratio or falling rate. If you cycled that set-up you would see that at full bump the shock would be doing almost nothing. Exactly what you don't want.
There are a couple ways to get around this without major butchery. Some of them are pretty complex, some are not. Trailers are one place rotary dampers would be really useful.