Ground loading trailers.

[psych0hans]

Hi guys, I'm currently building a ground loading trailer, loosely based on some designs I saw online. I have a client who needs a two bike trailer, but it should be less than 6' wide. I have seen some pictures online, but I don't really understand how I can make it work without a proper suspension. The one I have made has a double outer frame, so I was able to fabricate an independent suspension for it, but if I do the same for two bikes, it's gonna be way too wide. Can anyone tell me how these trailers would work?

[kd8cgo]

At first glance, it looks like a leaf sprung trailing arm setup with that curved axle piece, but I do not think that is how they work. I think the curved piece is not fully fixed at the front/along the axle. Rather, it just rides in non-load bearing carriers or straps that allow it to move to facilitate the trailer to drop the bed down. The long curved axle piece is probably not fixed to the drop down part with a bearing or hinge,and can probably slide backwards and forwards a bit. Those look like they do not work if they are hooked to the TV, they would need to be unhitched to drop the rear down to the ground, like they show. The curved axle is probably there for nothing more than lateral wheel spacing and wheel alignment or camber.

For a different design you can look at manlift trailers that drop down to the ground, their stub axle setups use leaf springs top and bottom or torsion stub axles to keep the axle stubs pointed in the right direction. Maybe you used torsion stubs on your first independent suspension design though and found them too wide?

I tried to find some large pictures to demonstrate the mechanisms:





This type of stub axle from eTrailer.com uses very little width on the trailer frame, but they are expensive:

[pchast]

If you go a little longer and stager where the wheel chocks are to
avoid interfering handlebars you can go much closer. They would
need to be loaded in order though.

[KCStudly]

I agree that it looks like the center/front of the bowed axle must be allowed to slide or float slightly, but it also looks like where it attaches to the spindles is a pivot bearing joint of sorts.

Curious, I had not seen this type of setup before.

[working on it]

Here's a link to a u-tube of a Lo-Riser trailer in action :https://www.youtube.com/watch?v=WqWQDFoP07k

[Dale M.]

Its a dual pivot system.... First the "axle" pivots in a bearing holder attached to the spring... The second pivot is at rear of trailer ... When the winch pulls the front of trailer down (into tow position) the axle articulates ....Essentially all hoop section of axle does is allow bed to pass through "normal" axle centerline and drop to ground....

17042010083.jpg (95.59 KiB) Viewed 1785 times

Also at rear of trailer the bed has to pivot (hinge) on the rear cross bar to cause the articulation of axle...

17042010087.jpg (101.67 KiB) Viewed 1784 times

I think the key to system that is not obvious is the center section of trailer is not connected solid to axle (hoop) but is allowed to move forward/backwards to allow articulation, the key to system is when bed is in up position it is locked to front of frame and bed and outer frame becomes a single unit that rides on springs as "normal" trailer.... As mentioned above trailer has to be disconnected from tow vehicle to allow full articulation...

Dale

[KCStudly]

So when the triangle between the hub center, rear pivot and axle bow pivot goes flat the spring shackles take up the difference in length? Something has to give.

[Dale M.]

So when the triangle between the hub center, rear pivot and axle bow pivot goes flat the spring shackles take up the difference in length? Something has to give.

Hoop section of axle is not connected rigid to bed but is probably in some sort of slot just to retain it (and allow it to rotate) .... Also the hoop section is as just a extremely dropped axle which allows center line of axle to drop all the way to the ground....

Replacing bar axle and springs with the axle shown below would accomplish same thing because there is no rigid axle across width of trailer...



Dale

[Matt]

Have you looked at ice house trailers? They use removable pins on the leaf springs to then lower the frame to the ground.
Something like this might also be used to mostly lower a standee to fit a garage.

http://www.fishhousesupply.com/icehousekits.htm

http://www.roadkingoutdoors.com/trailers.html

Hope this helps.

Matt

[psych0hans]

Hi guys, thank you all for your replies. I would love nothing more than using the Timbren axless suspension units, but I really can't afford that. The trailer needs to have an overall width of less than 6' and the bed width needs to be 5'. That really leaves me with very little room to play about with. I really like the idea of the road king trailers, but don't like the idea of having three separate winches to operate. I wonder if I can emulate the timbren system using a motorcycle mono shock or something like this...


I come from the school which believes in overbuilding everything, so I'm not too comfortable with the idea of having a suspension mounted on a single beam. The other trailer I made in this fashion had a double beam outer frame, so I was able to fabricate a working independent suspension for it. The same design will not work here because of the width constraints.







This build is on a very strict budget so fancy options are really out of the picture. I have ordered some suspension units from peak dynamics, based in the UK, maybe I can use those?

[kd8cgo]

Those type or torsion units would work if they are under 6" per side given your requirements, did you get the dimensions before you ordered them? They look longer than 6" from the picture but that can be deceiving.

If you cut those stub torsion axles down, it lowers the effective spring rate and load handling capability. also, if you cut so much off that you lose some of the mounting flange, it can put too much torsional stress on the designed fasteners and steel thickness used in the axle. This also will cause them to try to "pry" themselves off the trailer frame, which can fatigue both the stub axle and the frame, possibly breaking over time. Even just cutting the extra "square" portion off the inside, can cause the torsion action to try to make the square outside tubing "round", because the forces are concentrated over a smaller area.

You can use those type of motorcycle coilovers with the right sprint rate and a trailing arm like your first trailer, instead of the car-size coil springs. I saw you mentioned this and it should work fine as long as you size them right and don't put too much mechanical leverage in the trailing arm, vs. the coil spring rate. You might have to sacrifice some wheel travel to design it right to match the springs, but trailers usually don't need a lot to begin with.

I assume you meant the 6 foot overall width was not including tires and wheels? A 5' wide bed with a 6' wide overall including tires is hard to do using normal axles and wheels! (Without going to a bed-over axle design)

edit: I just had another thought, since you are making a motorcycle trailer. You can mount the guide rails at an angle to each other instead of parallel, in a V shape. This way you can make the rear of the trailer narrower than the front, and mount the axles back further, which will give you more room for your preferred suspension. It shouldn't cause much trouble loading or unloading, as long as the handle bars are above the seat and rear fender height of the bikes. You would have to carefully manage suspension height if you designed it like your first trailer, as putting the axle back much further will make the tongue shoot to the moon when you drop the bed if you have a tall suspension. If you make it low slung enough, it won't be as much trouble.

[psych0hans]

Those type or torsion units would work if they are under 6" per side given your requirements, did you get the dimensions before you ordered them? They look longer than 6" from the picture but that can be deceiving.

If you cut those stub torsion axles down, it lowers the effective spring rate and load handling capability. also, if you cut so much off that you lose some of the mounting flange, it can put too much torsional stress on the designed fasteners and steel thickness used in the axle. This also will cause them to try to "pry" themselves off the trailer frame, which can fatigue both the stub axle and the frame, possibly breaking over time. Even just cutting the extra "square" portion off the inside, can cause the torsion action to try to make the square outside tubing "round", because the forces are concentrated over a smaller area.

You can use those type of motorcycle coilovers with the right sprint rate and a trailing arm like your first trailer, instead of the car-size coil springs. I saw you mentioned this and it should work fine as long as you size them right and don't put too much mechanical leverage in the trailing arm, vs. the coil spring rate. You might have to sacrifice some wheel travel to design it right to match the springs, but trailers usually don't need a lot to begin with.

I assume you meant the 6 foot overall width was not including tires and wheels? A 5' wide bed with a 6' wide overall including tires is hard to do using normal axles and wheels! (Without going to a bed-over axle design)

edit: I just had another thought, since you are making a motorcycle trailer. You can mount the guide rails at an angle to each other instead of parallel, in a V shape. This way you can make the rear of the trailer narrower than the front, and mount the axles back further, which will give you more room for your preferred suspension. It shouldn't cause much trouble loading or unloading, as long as the handle bars are above the seat and rear fender height of the bikes. You would have to carefully manage suspension height if you designed it like your first trailer, as putting the axle back much further will make the tongue shoot to the moon when you drop the bed if you have a tall suspension. If you make it low slung enough, it won't be as much trouble.

Hi, Thanks for your detailed reply. Unfortunately for me, the width is including the tires. I don't think it's too feasible to use the torsion axles for a ground loading trailer, as they are about 12" long, not including the trailing arm and hub. I'm going to drop the idea till I can get my customer to pay for the Timbren unit, because I really don't want to risk fabricating a weak suspension system. So what I'm going to do is use the torsion axles and give him a really low loading height and a really wide fixed ramp so he can just ride his bike up.

Though this project isn't over yet. I'll keep working on it and post my results here. I really like your idea of loading the bikes at an angle, and it might just be the trick to get it working. But that will have to wait till mid October, as I'm traveling till then.