Trailer suspension

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Mar 20, 2017
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484
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Sonora, CA
I've built multiple trailers, each with leaf spring suspension. A couple have had shocks, some without. All have been various utility style trailers, some with boxes. Each one I've built has a limited suspension travel when loaded, due to the leaves, and tend to bounce over obstacles rather than absorb the impact, even those with shocks.

I have tried some longer leaf springs with better results, however, I'm still not satisfied. I've seen random photos over the years, here and other places, of wishbone or independent suspension. Just curious how those perform, both loaded and unloaded.

I scored some junkyard MacPherson struts for free from an early 2000s Corolla that still have considerable life, and am tossing around the idea of incorporating them into an independent suspension/wishbone style suspension. However, Mac struts (and arms) are run perpendicular to the road (articulating to the side of the vehicle), while I'm considering running them in line with the road. I don't anticipate issues with the orientation, however, I'd like to get the experienced opinions.

I realize I will need to have a pivot on the top mount and bottom, to allow articulation, which is contrary to how a Mac strut is normally mounted. Are there any foreseeable issues with my pivot-mount idea?

I currently have a flatbed trailer that I built a few years ago, with a leaf sprung single axle, that I'm planning on building a box for, and turning into an off-road camper. It won't see too rough of roads, however, I want to design it to where I can take it down fire roads or other western state forest roads and not worry about eggs breaking, or the whole thing rattling apart in the process. I'm hoping to use the Corolla struts, and changing the axle configuration to an independent suspension split "axle".

All thoughts are welcome. Trying to keep the parts cheap, serviceable and readily available.
 

ntsqd

technerd
Joined
Apr 26, 2007
Messages
6,392
Location
Upper So. CA
There was a guy on Expo who built a trailer using struts from something. It predates their server failure (or whatever it was that happened) though, so I'm not sure if that thread was recovered. He built it to be really light because he was towing it with something like a Geo Tracker.

Trailers do not articulate. Instead they will rotate about their coupler at the tow vehicle. The coupler and the tires are their 3 points of contact and those define a plane. There is no fourth point of contact that would cause or force articulation. That contact plane will rotate and twist instead.
Building a trailer with a long travel suspension is a waste of time and effort and can result in a trailer that is unstable. Building it with a supple suspension that is well damped so it doesn't break the eggs and foam the beer is worth the time and effort. In this design I used 6" stroke coil-overs placed behind the axle so it *might* have 7" of total wheel travel (haven't done the math to see what it really is and not sure that I ever will): I built a M416-101, sort of - https://forum.ih8mud.com/threads/i-built-a-m416-101-sort-of.1287354/

Do you have just the strut inserts or the whole assemblies with wheel hubs etc.? There is a bearing in the top mount of the struts. Usually they are a rubber mount and tend to be rather large. You could buy some racing camber plates for the original application and use only the part of them with the bearing to make the packaging easier. They usually use a spherical bearing. Or fabricate a clone of just that part. The trailer frame will need to have structure to support the full weight of the loaded trailer up at these bearings. That structure will need to be rigid enough to not fail under the impulse loads of potholes etc.

A concern if you have out to the wheel hubs and plan on using all of it is the bearing size. The reason that folks are advised to use 3500 lbs+ axles under off-road trailers isn't for the loading, it's because the lighter axles have smaller bearings and those don't tend to live very long in an off-road environment. I would have the same concern about using the wheel bearings from a small car.

Typically strut springs have a large OD. If you're going to run a tire OD usual for off pavement service they may want to share the same space. Spacing the tires further out may result in a trailer track width that is wider than desired and will put eccentric loads on the wheel bearings. The easy, but costly way to deal with this is to buy one of the threaded tubes made for racing use that are intended for adjusting the ride height and use racing coil-over springs instead. These springs have a lot smaller OD and will make packaging easier. Or you could make new spring seats that use the coil-over springs and weld them the strut enclosure. The advantage of using the coil-over springs is that most vendors will, as long as you don't cosmetically damage them, exchange the springs until you get the spring rate that you need.
 
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