Toy Hauler Frames

Bob E. wrote:
Thanks guys. Like I said, as a structural engineer, I don't have a problem sizing up the beams, welds and other connections for the loads. I might even put this thing into STAAD just for fun. I just don't know what sort of "safety factors" they build into the design since they are designed to travel down the road at 70+mph. I'm used to highway/bridge codes. Based on my calculations, it seems that I'm in the ball park compared to factory-built campers.

Surprisingly, my camper has a GVWR of almost 8,000lbs as-is according to the title. But it didn't feel anywhere near that heavy towing it home. I just picked it up last night, so I haven't had time to go find the actual weight sticker yet, if it even still exists. The beams under my camper are a standard C6 rolled section. I'm actually thinking of buying a couple C6x10.5 beams and stacking them under the original frame rails with longitudinal welds down each side, making a 12" "E" shape, and then add bracing as appropriate. This would provide the same structural section as a W12x14, although slightly heavier. This should be more than enough. In this configuration, the longitudinal welds will see very small loads since they are at the center of gravity of the section. So they are not all that critical. And since the legs of the "E" point to the outside, this will make the bracing design simple. Now I just need to investigate the tongue. It appears to be the same 2x6 tube steel as my dad's camper. So it might be ok as-is. But I'll have to double-check the thickness. Then I'll need to analyze the connection to the main frame to make sure it is solid enough to support the heavier tongue weight I'll have when I'm done.

I think if it were me I use some 2x4x1/4 or 2x6x1/4 tube under the channel frame you have now. I believe the 2x6 tube would be stronger than another pc of channel below your existing frame. I would also weld some vertical straps or angles in several locations down the length of your existing channel just to prevent it from trying to roll or fold on itself or weld some stiffeners on the inside covering both the existing and new. Just a thought.

Thanks guys. Like I said, as a structural engineer, I don't have a problem sizing up the beams, welds and other connections for the loads. I might even put this thing into STAAD just for fun. I just don't know what sort of "safety factors" they build into the design since they are designed to travel down the road at 70+mph. I'm used to highway/bridge codes. Based on my calculations, it seems that I'm in the ball park compared to factory-built campers.

Surprisingly, my camper has a GVWR of almost 8,000lbs as-is according to the title. But it didn't feel anywhere near that heavy towing it home. I just picked it up last night, so I haven't had time to go find the actual weight sticker yet, if it even still exists. The beams under my camper are a standard C6 rolled section. I'm actually thinking of buying a couple C6x10.5 beams and stacking them under the original frame rails with longitudinal welds down each side, making a 12" "E" shape, and then add bracing as appropriate. This would provide the same structural section as a W12x14, although slightly heavier. This should be more than enough. In this configuration, the longitudinal welds will see very small loads since they are at the center of gravity of the section. So they are not all that critical. And since the legs of the "E" point to the outside, this will make the bracing design simple. Now I just need to investigate the tongue. It appears to be the same 2x6 tube steel as my dad's camper. So it might be ok as-is. But I'll have to double-check the thickness. Then I'll need to analyze the connection to the main frame to make sure it is solid enough to support the heavier tongue weight I'll have when I'm done.

Buy an enclosed trailer of your liking and use all the tanks, plumbing and electrical out of your camper now. You will thank me later.

My 10K lb rated enclosed trailer is built on 10" beams - I would not want less on a toy hauler.

Most 5th wheel toy haulers in that range have a 10-12" I-beam but not like one used in construction, these have only 2.5-3" flanges and are much lighter in lbs per foot than a normal I-beams. As long as you have enough truck don't worry about weight and build one that is heavier than you think you need, definitely don't skimp there. On a bumper pull I think most are in the 8-10" range. If you look at a bare frame used on even the larger toyhaulers before they start building the box on them, its kinda scary how they are able to hold the weight they are rated for. They wiggle and wobble, sway back and forth and just feel really flimsy. If I were building one personally, I would start with a gooseneck or a deck over bumper pull as they are substantially built and build the box from there. I think by the time you try and rebuild your TT to the specs you need, you'd be better off buying a built deck over trailer and starting your build from there. Don't try and reinvent the wheel so to speak.

Yeah. I was looking at my AISC Steel manuals here at work. But they could be some Chinese steel section or something. Or, if Lippert or whoever builds these frames have enough volume, they may even have their own custom shape rolled to their specs.

You might drop by a local equipment trailer like a Kaufman....PJ trailers....Starlite.....Big Tex/etc and look at their same size gvw bumper pull/pintle hitch frames. They will be heavier built as they have no sidewalls to help support its gvw.
You may already have some type publication for AISI steel structures. Your odd size beam may be a import....with different mfg specs.

Thanks! I'll look at NATM and RVIA and see if I can find anything on specs. I did get out and measure my dad's frame on his Jayco Eagle travel trailer. Its not a toy hauler, but it is similar size and pretty heavy. That trailer actually has 10" I-beams, but only 2x6 box tube tongue. And the I-beams must be specially made because the flange width's (2.75") don't match anything in my beam charts. They look like they are rolled beams rather than fabricated/welded. But I don't know if they took a standard W10 shape and trimmed the flanges to save some weight or what. I'll have to crawl under there with some micrometers and try and get flange and web thicknesses and see what they actually are.

Most new RV trailers today have a enclosed under belly making the main frame rails almost impossible to see. Even if the main frame rails can be seen most folks wouldn't know the foot per pound weight just by looking.

RV trailers sidewalls figure into the load carrying ability unlike a flatdeck or equipment trailer.

Many of the equipment trailers websites can have the I beam foot per lb weights for their advertized gvw trailers.

You also might do a 1-800 or a email to some of the toy hauler mfg for info on the I beam size in the gvw your shooting for.

I haven't looked but NATM or RVIA webs may have builders specs.

Thanks for the reply. Yeah, I know that the frame isn't going to be strong enough as-is. I plan to beef it up. It only has a 6" c-channel frame now. Assuming the total loaded trailer weight is about 15000 ( I actually think it will be around 10,000-12,000 loaded, but I'm being conservative), I figure I'd need the equivalent of a heavier 8" I-beam or a lighter 10" I-beam. I just wanted to make sure that was in the ballpark of what the factories are using. I'm comfortable calculating the loads and required beam section properties. I just don't know what kind of "safety factors" they use.