sliding axles

[tj0llll0]

I want to build a trailer that is multifunctional. I would like to build a teardrop, but also be able to put a motorcycle rack on the rear. Has anyone here built their trailer with sliding axles for a variety of loads? The bike and rack are going to add about 300#s to the rear and I would like to be able to keep the tongue weight in spec within a reasonable margin. The tow vehicle will be a JEEP TJ.

John in Vegas

[toypusher]

I've never done that, but it sure seems plausible. Just mount the axle with multiple mounting locations, then bolt it into place for the perticular application that you are planning to use it for. I guess you could get fancy and create a single locking device to move it back and forth.

[PaulC]

I guess it depends on how far offroad you're thinking of taking it. I, personally, think it's just another piece that can let go.
Cheers
Paul

[JIML1943]

It is very possible my td is built on a boat trailer the factory built it's spring hangers on 2x2 angle iron the length of the springs with 3/8" holes on each end, the frame has holes every 4" so the axle can be moved fore and aft.
Hope this helps.

[eamarquardt]

Yes, I've built a trailer with a moveable axle. I've never moved it however. I'm building a teardrop now and the axle will be moveable. Here is a picture of the way it will be (I've fabricated some of the parts already). Let me know if you have any other questions.

Given that the load from the springs is spread along a larger portion of the rectangular tube frame, it should be stronger than just welding the spring hangers to the tube. Also the angle iron is thicker (stronger) than the frame. Just slide the axle till you get the balance you desire, mark, drill, insert the strap nut from the rear of the frame tube, and install the bolts. If your frame has a sharp corner you can mill out the radius on the angle so it will bolt up to angle or channel iron (tubing with it's radiused corners doesn't have this problem). See my album for picutures of a trailer with a channel iron frame and a moveable axle.
Cheers,

Gus

[angib]

Smaller boat trailers over here hold the axle cross member to the frame rails using square U-bolts - an angle is welded to the cross member either side of where the frame rail will go, for the U-bolt to clamp.

Too hard to explain, so I'll do a diagram.



One more thing to consider is that moving the axle will solve the balance problem of putting a motorcycle at the back of the trailer, but it doesn't solve the pendulum problem - that's still a lot of weight hanging out the back, trying to start a sway. With enough tongue weight, I doubt it's a serious problem, but that's not guaranteed.

Andrew

[eamarquardt]

The trailer can be considered a mass with a center of gravity (mass). The axle is placed behind the center of gravity so that you get weight on the tongue which means the center of gravity/mass is in front of the axle. It doesn't really matter what is hanging out how far (within reasonable limits and if everything is rigid). So, if you have the correct balance, how the load is physically placed isn't important. Not entirely trusting my own memory of the laws of physics, I verified the above with my brother-in-law who is a bona fide rocket scientist (phd mechanincal engineering, UCLA and has worked at Rockedyne for 34 years). So, you (and I as I plan on doing the same thing with an extendable motorcycle ramp, see album) should be fine as long as the tongue weight is appropriate.

Cheers,

Gus

[tj0llll0]

Thanks guys. I kind of just jumped into this. I got the bug to build a trailer, started thinking of the requirements I wanted to address and had many ideas twirling around my head and stumbled onto this forum (great forum btw). I havent really sat down and done any serious planning yet. I thought about the sliders because Ive used them on the big rigs and thought that would solve most of my weight problems. I even figured it would solve the axle placement/ door interference because when I got where I was going I could just slide the wheels out of the way. I am looking at a pic of a TD now and realize it would probably be impractacle to be sliding the axles with any frequency because of how low to the ground they sit. I think I will have to keep on reading here and put some serious time into the planning of this project.

John in Vegas

[eamarquardt]

Your comment about interference between the fenders and the doors was one that I have already addressed. I didn't figure there'd be a problem with the doors to the cabin, but that there might be a problem with some doors to a storage area I plan to have between the galley and the cabin. I "solved" this problem by designing the storage doors high enough to clear the fenders. But............, if it were really easy to move the axles when you arrived at your destination, the doors, could be made bigger to improve access to the storage area. Soooo, you've got me thinking on how this might be done to achieve the "perfect compromise" (an oxymoron because a compromise trades one thing for another so is therefore less than perfect in a least one respect if not all respects).

I'll go back to thinking about it now.

Cheers,

Gus

[angib]

Gus, as your brother has a Phd in mech eng, he really has no excuse for overlooking moments of inertia (though he may want to use a more technical name for them!).

A trailer with all its weight carried near the axle has a low moment of inertia (just like a mid-engined sports car), while a trailer with all its weight carried at the front and back extremities has a big moment of inertia - when that starts to sway, the big inertia helps keep it going or make it worse.

There are two reasons why every towing guide ever written says to pack loads over the axle - balance and inertia.

Andrew

[jimqpublic]

I'll take a moment to comment while this thread has some inertia going.

My grandparents retired in 1965 and were ready to roll to Alaska with their new 4x4 pickup and Alaskan popup camper. His work buddies bought him a Honda Trail 90 motorcycle as a retirement present. With only a few days to departure Gramps had a rear carrier fabricated to carry the bike.

Unfortunately he had to lift the bike off in order to open the camper door. In three months of travel the bike got ridden about a half dozen times. In fact when making one big loop they left the honda at a gas station for a few weeks since it was a PIA.

Was there a point to this message? Oh yeah. With a rear-opening kitchen you'll have to remove the bike to make lunch. You'll have to remove the rack to avoid banging your shins while making said lunch.

I would say go with a front mount rack for the bike and aim for slightly low - but still reasonable tongue weight with the rack empty. Loaded it might be a bit high but isn't that what overload springs are for? With the axle about at the cabin center and a 5' tongue (including bike platform) roughly half of the bike weight would go to the hitch ball. So if the no-bike tongue weight is 100 pounds it would go up to 250 loaded.

Re- Sliding axle- How about a sliding cabin instead? Use a platform type trailer with gear tie down tracks. Build the teardrop to ride in the tracks on rollers with locking pins to hold it in place. I think an airplane salvage yard might have something...

[eamarquardt]

Beats the heck out of me! Put another call in to the rocket scientist. When I get the answer, I'll post the rocket scientist view (he'll check with other rocket scientists I'm sure). The sliding bumper/ramp is fabricated. See album. You, however have a point about removing the bike to access the galley and have now caused me considerable consternation. Thanks. As I haven't welded the frame up just yet, rethink the "plan". The bumper will fold down to access the galley, but doing that is not much more trouble than opening the hatch, so it's not much of a concern. Will keep you posted with answers and thoughts. I don't want to put the bike in front of the cabin cause I plan to install a box, it's exact function is, at this point, highly secret (I'd tell you but then I'd have to "off" you).

I'll be back.

Cheers,

Gus

[madjack]

...if you look at the Little Guy Sport, the rack is in front of the cabin for carring bikes or 4wheelers...in Sandmans pics of the one he got, there is a front box in front of the rack...most all of the weight in the box will be on the tongue, helping to keep a proper balance when a bike is not on the rack...as a former 2million mile trucker, the sliders on the trailer were always a real pita to operate...an adjustable axle onna tear would be tougher since the ground clearance is so low...adjusting at the house before use would not be too bad but I wouldn't want to havvta keep adjusting the axle, while using the trailer, just to get in the door...think MAJOR PITA.........
madjack

[Wright]

And my son wonders why I call him Pita....

[nitromethane43]

An easy way to have movable axles is to replicate the system used on box trailers. You can add an channel under the frame along with a series of drilled holes for a hitch pin or spring latch, the frame must be substantial enough to support the load without being pushed to the limit with holes drilled in it. Here's a rough drawing on how it can be done. Fenders can also be attached to the bottom of the channel moving them along with the axle.