Small Travel Trailer Frame Design Question

[jerlands]

The moment of inertia of those HSS sections will give you an idea of the relative strength and stiffness.
1x2x0.083 wall the moment of inertia is 0.2379 in^4
1x2x0.120 wall it is 0.3214 in^4
2x3x0.83 wall it is 1.021 in^4
So the 2x3 is more than 3 times the strength and stiffness of the 0.120 wall 1x2

It is your trailer for your use, but if you are going to the trouble of building, it costs little more to make it a couple feet longer. Even when I was tent camping I kept finding the list of gear growing all the time. So what you think might be big enough, may be too small after a few trips. Also - you might want to rent or borrow the smallest trailer you can find for an hour or two and find out how painful it can be to have to back up a short trailer. Longer is so much easier.

And just in case you wanted to know.
2x2x0.083 has a moment of inertia of 0.3905 in^4 and
2x2x0.120 wall it is 0.5337 in^4

So the 2x3x.083 would be lighter than 2x2x.120 wall but almost twice as strong in the vertical direction.

I was able to plug in some numbers (not that I understand what I'm looking at) and came up with 1.467 in^4 for .120 2X3 which is about 40% more strength than .083 2X4 at approximately 30% weight gain. Ideally I think .083 2X3 works best for my situation but because I am building it I want to err on the side of caution. I'll bite 40 lbs. on this build but if I do another in the future for off road the frame will be 2' longer and the tongue will sit beneath the cargo frame. The temptation to enlarge the frame is prevented by my desire to keep the towing weight of the trailer loaded at around 1000 lbs and which will limit me to about 550 lbs of cargo. I do have 14" just ahead of the cargo box and storage on the lid so i think i'm gonna have to learn to live with this and use the experience i gain for another project. As for backing up... that is going to be a lesson for me also... i drove a ton of farm equipment as a kid but that was then and this is now...

[drhill]

yes, the 2x3x.083 wall will be plenty strong. For reference, my trailer is 5' x 10' deck and the side beams are C3 x 4.1 lbs/ft and the moment of inertia is 1.66 in^4. But it is a heavy trailer and also used as a utility trailer with the camper removed. It will easily haul 100 cu ft of green firewood or a yard of gravel or 40 bundles of shingles. I also went heavy weight as I don't do well stick welding thin metal. Have fun building.

[jerlands]

yes, the 2x3x.083 wall will be plenty strong. For reference, my trailer is 5' x 10' deck and the side beams are C3 x 4.1 lbs/ft and the moment of inertia is 1.66 in^4. But it is a heavy trailer and also used as a utility trailer with the camper removed. It will easily haul 100 cu ft of green firewood or a yard of gravel or 40 bundles of shingles. I also went heavy weight as I don't do well stick welding thin metal. Have fun building.

Once I begin to understand a little more about the different measurements for steel I'll probably be able to make better selections, as well as give me something else to play with. I've now downloaded charts with major axis calculations but that's about as far as I am right now. So thanks for the feedback and once I finish I'll post the results...

[saywhatthat]

frames have become like lies of man hood .'' mine is bigger than yours if you can find some of .angib.pwp.blueyonder frames here there light cost affect . OH by the way my trailer frame is 16'' I beam 2 in. thick to hall a 100 lbs

[gudmund]

just to throw another idea into the build - saw it just last nite when reading Tony's 'teardrop build book' (great book!!!) Question: could his removable tongue be used, making it 'adjustable' in length?? (and thus also removeable for security when parked/stored) A few years ago after selling my old teardrop which had had a 4 1/2ft long tongue and figuring it 'wouldn't be that big of a deal' with the new one being 4ft long (6 inches shorter) and yes, was I wrong!! I today, still miss the longer tongue!! Just an idea = make it 'totally' adjustable...….

[jerlands]

just to throw another idea into the build - saw it just last nite when reading Tony's 'teardrop build book' (great book!!!) Question: could his removable tongue be used, making it 'adjustable' in length?? (and thus also removeable for security when parked/stored) A few years ago after selling my old teardrop which had had a 4 1/2ft long tongue and figuring it 'wouldn't be that big of a deal' with the new one being 4ft long (6 inches shorter) and yes, was I wrong!! I today, still miss the longer tongue!! Just an idea = make it 'totally' adjustable...….

Amazon's preview of the book I guess didn't include the removable tongue? I've seen versions of a removable tongue but i'm not sure how it would benefit me?... I think the defining feature in trailer stability outside of the quality of build and balance (center of balance in relation to everything else) is the length from the hitch to the trailer axle and that ratio between tongue length and cargo length... the tongue itself to me is just an attachment point to the frame and as long as it doesn't get in the way while turning my aim is to make it strong and secure...
EDIT: actually... the towing vehicle has a lot to do with the trailer's design... Hitch Your Trailer: How Trailer Length Affects Towing Stability https://www.streetdirectory.com/travel_guide/215518/rvs/hitch_your_trailer_how_trailer_length_affects_towing_stability.html#:~:text=As%20a%20general%20guideline%20I,of%20at%20least%20110%20inches.

[jerlands]

just to throw another idea into the build - saw it just last nite when reading Tony's 'teardrop build book' (great book!!!) Question: could his removable tongue be used, making it 'adjustable' in length?? (and thus also removeable for security when parked/stored) A few years ago after selling my old teardrop which had had a 4 1/2ft long tongue and figuring it 'wouldn't be that big of a deal' with the new one being 4ft long (6 inches shorter) and yes, was I wrong!! I today, still miss the longer tongue!! Just an idea = make it 'totally' adjustable...….

To be downright honest about this thing... I am concerned about the trailer's stability being such a short distance from the trailer axle to the hitch point.. which is only 87" (7'3".) The trailer overall is 18" longer (105" or 8'8") but the tow vehicle it is designed for (a Prius) has a wheelbase of 106". I'm uncertain how all these factors are going to interplay but it looks like I'm going to find out.

[jerlands]

just to throw another idea into the build - saw it just last nite when reading Tony's 'teardrop build book' (great book!!!) Question: could his removable tongue be used, making it 'adjustable' in length?? (and thus also removeable for security when parked/stored) A few years ago after selling my old teardrop which had had a 4 1/2ft long tongue and figuring it 'wouldn't be that big of a deal' with the new one being 4ft long (6 inches shorter) and yes, was I wrong!! I today, still miss the longer tongue!! Just an idea = make it 'totally' adjustable...….

yeah... I think I'm so concerned about the short length of the distance from the hitch to the center of the axle I'm going to lengthen the center tongue rail by another foot.

[gudmund]

the length could be adjustable - depending on how many adjustment holes you were to drill in the trailer side 'receiver'. Each hole drilled will create a different towing/backing feel along with just making for a shorter garaged trailer when parked/secure. (Say a 4 ft fixed tongue with a 'adjustable' 2ft trailer receiver.) I do know that a longer tongue makes for a ''less tail wagging" incident when having to take an 'evasive' move when towing. I would think after a few tow 'adjustments', you would find 'your' favorite adjustment hole's for driving/backing. Just something more to thing about being still 'early' in the plan for a build. PS. the receiver that you see in Tony Latham's book that he used is available in different lengths - I have a 1ft long one mounted on the side edge of my trailer for a umbrella holder along with a 2ft long one centered under the back of the trailer for the cycle rack. Amazon carries them. Not that it is going to matter, but years ago I asked a dump truck driver why the trailers they were towing had such long 'adjustable length' tongue's on them? The answer was that they could tow/carry "more" weight with them..... Take care.....

[Tomterrific]

I'm not going to be any fun. Go buy a small Harbor Freight trailer. Proven light weight design. Make the box low, long and narrow for less wind resistance, the highway speed killer.

A mistake with gussets is to put them in the center of the tube. This makes a "knee" for the tube to bend and collapse over. Put a sheet gusset at the neutral bend line in round tube or at the edge in square tube. Best to use the same size tube and make a triangle for maximum strength.

Tt

[tony.latham]

Go buy a ...

Tom! This guy can fabricate. He can cut steel and weld. He's a maker.



Tony

[RJ Howell]

Two alterations I've made so far in the design. 1.) I increased the tongue length 1.5' beyond where it had originally formed but also shorted the back end so I could have one continuous member across the frame at the center of the cargo box. The shaded area's highlight this. I've also moved the axle back 2" tentatively until I can measure tongue weight. It is however about as far back as it can go due to the fender intruding on the bumper.

I'm a bigger fan of this design. The tongue box (when loaded) should give you that 12% tongue weight you want for stability. Not sure why your hesitating on running that tongue bar under the box frame? It's makes the Box frame stronger (not sectioned) and a better weld spot for the tongue bar at the front of the box.

Good to see you're working through all this before just jumping in!

[jerlands]

I'm not going to be any fun. Go buy a small Harbor Freight trailer. Proven light weight design. Make the box low, long and narrow for less wind resistance, the highway speed killer.

A mistake with gussets is to put them in the center of the tube. This makes a "knee" for the tube to bend and collapse over. Put a sheet gusset at the neutral bend line in round tube or at the edge in square tube. Best to use the same size tube and make a triangle for maximum strength.

Tt

The point of the build is not just to have but to endeavor and prevail... I've looked into gusset design and options and have yet to make any solid design consideration but one of my resources has been https://mechanicalelements.com/strengthen-a-trailer-frame/ . I'm now leaning towards angle which gives me maybe the best of both worlds... I can weld it at the edge and still have additional support running down the beam...

[jerlands]

Not sure why your hesitating on running that tongue bar under the box frame? It's makes the Box frame stronger (not sectioned) and a better weld spot for the tongue bar at the front of the box.

The problem i had in placing the tongue under the frame is in keeping the frame to a dimension within my design considerations... it is designed to be pulled by a small vehicle like the Prius which I own and I want to limit the overall weight of the trailer at 1000 lbs max... placing the tongue underneath the frame enlarges the frame dimensions, minimally 24" but ideally it seems using what I've learned is called a wrapped tongue I'd be enlarging the frame more like 36". I simply cannot use that space.. http://trailersauce.com/information/draw-bar-design/trailer-drawbar-design-function/

[jerlands]

using 1/4" X 2" flat bar I believe I've come up with a solution for adequate joint support at my two area's of concern and also it will strengthen and help distribute the load at frame spring hanger points.