Coil-over trailer suspension chassis

[wattsworth]

Here's a light trailer chassis that would work nicely for a light teardrop. Its complete with an axle triangle like a Ford Model T, adjustable coil-over shocks with damping (from a motorcycle), and a Panhard rod to locate the axle properly. A very smooth ride. Instead of trying to describe it, here are pictures:

... the wood bar is for temporary lights to drive it home legally.

The total weight of this frame & suspension design as shown is 212# with a 10' tongue, 68" between the coil-over towers, 12" wheels, schedule 40 pipe, and 1/8” wall 2x3" square tube for the frame. About half of the weight is unsprung axle, wheels, & hubs. What can I say, I overbuild things and like safety factors over 4 above yield to account for fatigue and any other loads I forgot. I'm also quite particular about quality full-penetration welds and fully closing the tubes via welding to ensure no moist air can condense inside the frame and start rust from the inside out ... where you can't see it doing its damage.

This design assumes the trailer box is strong enough to support itself and can be mounted to the frame with about 6 bolts.

Certainly using drawn over mandrel (DOM) tube and thinner square tube would save perhaps 40# -- and add a lot of TIG welding. If I had the TIG stuff, I'd think about 4130 aircraft tubing. But, I'm limited to stick welding at the moment and build accordingly.

The forward axle connection to the tongue (apex of axle triangle) is a 1/2" tie-rod end between two brackets so the anchoring bolt is in double-shear. The tie-rod end is threaded into a rod at the apex of the axle triangle. It helps to have a lathe to turn such items, but I resort to a hand tap for the last bit.

This design would be about 10% lighter than the Harbor Freight trailer option, but it has adjustable suspension, and shock absorbers. At the end of the suspension travel there are rubber bumpers too.

A similar configuration could be made with longer-travel coil-over shocks for an extreme off-road build. Yet, the long travel coil-overs would only really help when the trailer has some inertia in roll relative to the tow vehicle. Basically a bump only on one trailer wheel would tend to rock the trailer side-to-side around the hitch ball. But if the trailer is heavy it would not correct for a second. For this short time, coil-over shocks would do their job and prevent the trailer from huge spring rebound.

[MidTNJasonF]

I really like the design. What is the source of the hub and axle configuration if you do not mind me asking? I happen to have a shelf full of coil over rear motorcycle shocks from previous projects.

[wattsworth]

The source was Northerntools.com. The axle stubs are item #1246W and hubs were item #204, with bearing buddies to keep the bearings greased like a boat trailer -- very convenient. The rest came from the local steel place and my welder.

[asianflava]

I like it!

Do you have a pic of the tongue where the trailing arms attach?

[wattsworth]

I would not call them 'trailing arms' ... the axle and the struts going foward to the tongue are welded together into one big solid triangle anchored under the tongue with a 1/2 inch tie rod end -- a 'ball in socket joint' that allows the axle triangle to hinge up and down as well as tilt/rotate relative to the frame. There are four contact points between the axle and frame:
1. The tie rod end at the apex of the axle triangle under the tongue
2. Both coil-over shock absorbers -- thats two points
3. The Panhard rod to locate the axle under the frame in the side-to-side direction

While the Panhard rod does move the axle side-to-side when the suspension compresses, the amount is so small it can be ignored. At full-stuff on the suspension, the axle moves sideways about 3/16th of an inch. My next trailer frame (for a small ultralight teardrop) will reduce this by about half with better geometry.

I'll get a picture of the tongue tie-rod joint soon ... at the moment I'm separated from the trailer by 1,000 miles.

The suspension is not independent. The axle triangle is a variation of how the suspension was engineered on the Ford Model T, except with coil-over shocks instead of a single transverse leaf spring directly over the axle.

[angib]

That's a very neat piece of work. One area of concern over here (and the US Pacific North West where I think it rains as much) is the exposed rod-ends. These have a very short lifespan when used in wet conditions, when grit can be dragged into the bearing surface. But then I guess a little slop in these bearings will have no negative effect.

There are sealed rod end bearings available but at a pretty horrific price.

Andrew

[wattsworth]

Thanks Andrew.

Yes, the front 1/2" tie rod end was about $27 with non-lubed teflon bearing. I was concerned about the bearing material being compromised over time and the ensuing slop allowing the housing to pop out over the center ball part and slip over the mounting bolt head -- freeing itself to the world. To minimize the danger, I was careful to enclose the tie rod end with a large washer so that it would not be possible for the housing to pop over the mounting bolt head and escape even if the bearing got toasted. These tie rod ends will need annual inspection, but that's good for the entire trailer too.

Yet these rod ends don't really move very much. If you're concerned with rust, you might want to consider a thru-bolt elastomeric joint with polyurethane to provide the compliance. I'm sure these would work just fine in your part of the world. Or, one of those lubricated rod ends used in automotive suspension systems and steering. Any number of these could be adapted for use in this design and work just as reliably as they do on cars and trucks.

Thanks for the pointer. I think I'll use elastomeric joints in my next trailer build.

[dguff]

Unless you want a cross bar intruding into the sleeping space at about your knees it looks like you would have to build the floor above that rear suspension crossmember. That would require large spacers and/or outriggers along the tongue to get the floor level with that crossmember. Then I would want some sort of extra stiffener to help support the walls behind the axle. Suddenly what appears to be a simple frame becomes a bit more complex.

Jerome

[wattsworth]

Jerome ... I think you missed the note on the wood 2x4 being a temporary light bar to legally drive home. The teardrop box would really sit on the steel frame between the shock absorber towers.

More photos as requested:

[kennyrayandersen]

It's certainly one way of solving the problem and it for sure looks mighty cool, but I don't think it will be lighter than a simple torsion axle and a a-frame FWIW.

[asianflava]

OK I see now. I from the first set of pics, I thought that each forward leg of the triangle was connected independently to the tongue.

[wattsworth]

The HF trailer weight in the ultralight topic was 227#. I don't know if Andrew has posted the weight of his ultralight TD A-frame trailer anywhere, but I have no doubt it would be lighter and easier to make.

For my build, I don't like the torsion axle idea for several reasons:
1. The axle tube is open to water entry with partial rubber blockage to dam it up inside and rust inside where you can't see it.
2. As with the evolution of off-road trailers mentioned elsewhere, the rubber works better that leaf springs (provides some damping) until the rubber is compromised and torsion part works it way out. That might never happen on the road, but my TD will go mildly offroad during it's lifetime.
3. Torsion axles are fabricated by freezing the four round rubber pieces with liquid nitrogen into a half-moon shape, placing them on the torsion square section steel part, and shoving all of it inside the axle square tube. These are not within the capabilities of the average shop -- definitely not mine. The entire axle has to be considered a disposable part. I'd prefer to have axle componets I can fix or service in the field.

Andrew's ultralight trailer frame is good for it's intended use, but I like fairly long tongues, closed beam sections, low deflection, and high safety factors. And creating a new and interesting design is just part of the fun of building your own.

[dguff]

The new pics make it much more clear. Thanks.
Jerome

[starleen2]

It's certainly one way of solving the problem and it for sure looks mighty cool, but I don't think it will be lighter than a simple torsion axle and a a-frame FWIW.

Sometimes thinking outside of what everyone else is doing gives rise to new innovations - I've read plenty of threads that have suggested using coil overs from different donor axles and prefab units - Finally one that looks sleek and functional - good job and thank for showing use a good example of trailer innovation.

[Dark Horse]

the chassis looks great, thanks for the pics