Non-military 20' Trailer Strengthening Advice

I picked up a trailer and started to strip it down to strengthen the frame, redo the axle, add brakes, and redo all the wiring. The first thing I need to figure out is how to strengthen the frame. Before taking it apart you could sit on the corner and the trailer would flex more than I want. Second thing I would like advice about is where to position an S-280 shelter on it. Should I center it, or put it to the front or back. I have taken many measurements and did some drawings of the current frame. Let me know what you think.

EDIT, T-chan is actually an I-beam. My mistake when doodling.

Its hard to tell from the one pic, but if your "A" frame runs under the main frame from as far back and as far wide as you can go, that helps a ton! Single axle, or dual? Weight rating? Manufacturer?

The A frame for the tongue does not go all the way back. In the third picture you'll see a box in the middle/front that doesn't have a center support and that's the only point that attaches to the a frame. I can extend it by taking it out to the sides. Trailer was hand built, dual 3500# axles.

ill get more pics.

The area that your springs mount could use some reinforcement and some X bracing in the frame would help. If your floor is steel, like diamond plate, welding it on will give a lot of strength. If using boards on the floor, full length would help (and be pricey at 20').

Assuming C-chan is C Channel. T-chan is T Channel? Can you get some pictures of this? A member with a T shaped cross section has no real structural value, and depending on it's dimensions and application, most likely needs another flange welded on it too make it an I-beam or if no other option a J channel.
As Gimp said extend the tongue out to the side rails.
Your drawing also makes the axles appear very narrow? Narrow axles are no fun!

tobyS said:

The area that your springs mount could use some reinforcement and some X bracing in the frame would help. If your floor is steel, like diamond plate, welding it on will give a lot of strength. If using boards on the floor, full length would help (and be pricey at 20').

Click to expand...

Floor is 2" x 8" wood planks across the short way, then 2 lag bolts per side holds it down.

Jbulach said:

Assuming C-chan is C Channel. T-chan is T Channel? Can you get some pictures of this? A member with a T shaped cross section has no real structural value, and depending on it's dimensions and application, most likely needs another flange welded on it too make it an I-beam or if no other option a J channel. As Gimp said extend the tongue out to the side rails. Your drawing also makes the axles appear very narrow? Narrow axles are no fun!

Click to expand...

EDIT: T-chan is actually an I-beam. Sorry for the confusion.

You are correct with the c-chan. I think what gimp recommended will be the biggest structural improvement by extended the a-frame to the sides and have it come further down the trailer. I just took two pictures of it and will upload them next.

See attached. I hope this shows how far the A-frame goes into the frame, it's not very far. If making the A-frame wider and bringing it to the rails and down the frame will be the biggest improvement I'll make it happen. Also someone mentioned axles, mine are very narrow as you can see in the first post. I can get new axles but it will cost quite a bit, but there's no way to mount them wider. I could have the wheels closer to the outside rail but the mounting point would still be narrow.

EDIT: In the picture with the axles, what if I weld in another piece of C-chan where I drew the tires and mounted the axles on that. That would give me a wide stance.

Personally, I wouldn't run my floor boards across. That gives very little strength. 20" wood is not cheap, but it is available.

It looks like a frame to axle mount reinforcement could go along the c channel and a couple feet beyond. I'd use a flat, maybe 8" wide and 5/16 thick.

How far is the spring perch on the axle from the wheel and tire? It looked farther than your new pictures appear.

Thanks for the advice on the floor boards.

I planned on replacing the brackets that support the axle. The spring perch is inches away from the brake flange, which is inches away from the wheel hub. The tire sits closer to the inside rail than it does to the outside.

Don't count on wood decking for structure.
What vehicle will you be towing this with? What will the trailers approximate loaded weight be?
What is the measurement from the ball hitch to the centerline between the two axles, then to the rear of the 20' deck?

Jbulach said:

Don't count on wood decking for structure.
What vehicle will you be towing this with? What will the trailers approximate loaded weight be?
What is the measurement from the ball hitch to the centerline between the two axles, then to the rear of the 20' deck?

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I didn't really think to use the wood for structure until someone brought it up. This will be towed with my F150 ecoboost and LMTV. The front attachment will be a c-channel where you can mount a pintle or a normal 2 5/16" (adjustable height). Loaded weight (including trailer weight) will be around 4200-5000 lbs with the shelter on it. Empty, the trailer should be around 2000-2200 lbs. Axles are dual 3500#. I will get measurements later today.

Any chance of wanting or willing to mount your shelter permeant? It could become the main structure of the trailer, but you still need to insure the tongue is strong enough.
I'm hoping you can mount the box all the way forward without gaining too much tongue weight for your F150.
Narrow axles still = bad, especially with a higher center of gravity

Jbulach said:

Any chance of wanting or willing to mount your shelter permeant? It could become the main structure of the trailer, but you still need to insure the tongue is strong enough.
I'm hoping you can mount the box all the way forward without gaining too much tongue weight for your F150.
Narrow axles still = bad, especially with a higher center of gravity

Click to expand...

The problem with the shelter is the fact it has "skids" on the bottom and I was just going to mount it with cables like they do on an LMTV sitting on top of the wood. As of right now the A-frame will be redesigned to extend to the sides and to go further into the main frame. I will also be looking into making the axle wider and to try and get the wheels/tires closer to the outside frame rail. I think the combination of these two things should make it stronger.

I have been told that the 'correct' weight of the hitch point should be no more than 15 percent of the total weight of the trailer with every thing in place. More than that will make it front heavy and difficult to control. And I've been told not enough weight on the hitch point helps the trailer go all over the road instead of following the towing vehicle. I certainly hope the trailer SME's soon give their opinions. My only question is - why a 20' trailer for a 12' box? I have an S-280 on an M-36, with enough room to carry 12 Scepter fuel cans in front of it and have 46" of rear deck behind the S-280. My opinion is that you should have your tires as close to the outside edge of the trailer as possible - no more than four inches from the outside edge of the trailer back in to the outside edge of the tire, and preferably about two or less. You want to be able to see the tires in your rear view mirrors so you have at least a little warning that something is amiss back there.

Honestly, I would skin the deck in sheet metal and re-do the tongue-"A" frame part for rigidity. I cannot comment on the axle placement or width.


How far off the ground is the tongue? Does it have any brakes?

You want the shelter to be centered over the trailer axles with slightly more weight on the tongue than towards the back.
The shelter itself will strengthen the trailer frame if you are going to permantly mount. I would set it on the open frame and weld the shelter to the frame at every cross bar, then you can deck the trailer from the shelter out.
Just my 2 cents, good luck! And above all, have fun!

Are you sure the trailer was flexing and not the springs or soft tires.

The main channel and cross members are not large enough for the length of the trailer.

The springs and I beams are to close together

What is the gvw of the trailer

Been a busy weekend. I got all the old axle hangers off and almost finished removing the a-frame. I have called my local metal shop and will pickup 2.5" x 4 box frame. Two 20' pieces will run down the sides underneath the bed that's already there and tie into the new front a-frame. Pretty much build another frame below the deck frame. The new wider axles will mount to the new box frame and put the tires about 3-4" from the outside of the trailer. This should solve the problem with the flexing and help with stance being wider. I have also bought electric brakes to go on these axles.

Going back to a couple of your questions. The trailer was dirt cheap so why not. 20' will leave me 6' to play around with to bring dirt bikes, atvs., or a have nice porch. The flexing is coming from the frame in general. I have almost everything off of it and can flex it pretty good right now. This will be solved with my new frame that I'll attach beneath it. I'll upload some photos as I go.

Couple pictures as I worked on it this weekend. I took off the old axle hangers, and started on the front A-frame. I got a bunch of parts today in the mail so I can't wait to start using new stuff.