Help with tongue strength

[48Rob]

I'm working with a 5 x 10 trailer built of 2 x 3 x 1/8" steel.
Tongue is attached at the first and second crossmember (30" from front of trailer to rear of second crossmember.)
Tongue is just a straight bar, also 2 x 3 x 1/8".
Tongue extends 66" from front of trailer.
Tongue is welded at front of trailer on sides only, full length (2")
Tongue is welded at rear crossmember on both sides (2") and across back (2").

Tongue weight is exactly 225 pounds.

Is this overloaded?

I've looked at the tongue strength chart, and the numbers are so far out, I have to wonder...
Trailer weight is in the 1500-2000# range (I'm going to try to get it to a scale in the next couple days.)

Rob

(Edit; Trailer weighs 1680 pounds, so loaded for camping, about 1800#
I don't have time before camping trip in a few days to replace tongue, any ideas for adding temporary tube, or angle, or channel to strengthen it up?
I can bolt something to the existing tongue, or tack a channel to the bottom of the tongue?)

[High Desert]

Rob, looking at the chart I found the same thing. Way out of range, like only 40% of recommended using a 1600# trl weight? Using the chart, it would seem that making it into a composite tongue reaching within a couple of feet of the hitch would bring the existing parts back closer to spec, but still close to max. Or am I completely misinterpreting the chart?

I feel a learning experience coming on...

[angib]

I guess it's about time I completely redid that tongue strength page so that it's obvious what assumptions it uses.

It's based on the Australian trailer rules and they are very strict/demanding. They are pretty simple and say that you have to be able to apply half the trailer weight as a force on the coupler (that is, with a big giant's hand holding the main frame still). The Australians have washboard roads and I think that is why they are so demanding.

At the time I first published those rules, there was a discussion about how over-the-top they were and particularly Cary of Camp-Inn gave his opinion of what works for them. As a result of this I suggested that for road use, half the Australian strength is enough, so that's a force of one quarter the total trailer weight on the end of the tongue.

In the last few weeks I've got the European/International standard for tongues and they say 24% of weight for unbraked trailers and 36% of weight for braked trailers -I think their idea is that brakes make the trailer pitch nose down and that increases the tongue load. They do however limit this to trailers with a tongue load under 10%, because that's a really heavy tongue by European practice.

So we're beginning to see a bit of a pattern here.

Your 2x3x1/8 single tongue on a long, long tongue of 66" allows a vertical load on the end of around 400 pounds (assuming the 3" is height). So that's about 22% of your 1800 pound trailer weight. So it just about passes the quarter-weight test.

For comparison, I understand Scamp 13ft trailers of 1200-2000 pounds weight have an A-frame tongue (so two members) of 3x1-1/2x1/8 and theirs is nothing like 66" long.

I think (just my opinion, not a statement of fact) this is a bit marginal for two reasons:
- I think the horizontal strength and stiffness may be too low on such a long single (not A-frame) tongue, so I wouldn't be surprised to hear the trailer had a shimmy problem caused by horizontal tongue flex;
- 30" to the second cross-member is quite short so there is going to be a huge load on both cross-members - the front one will have the trailer body above it, but I suspect the overall strength of the tongue will be limited by when the second cross-member fails, which may be sometime before the tongue fails.

Sorry to be negative, but I bet it's better to work this through now, rather than wait till you're finished!

A photo of the frame (or a photo of the drawing the frame was made from) would be good, just to check we are all talking about the same thing.

[48Rob]

Andrew,

Here is the frame before the cabin was installed;





You are quite correct that the trailer had a shimmy.
Not sure why the tongue is so long, I could easily remove 12-16" and still not hit it in a jackknife.
It had a bent axle too, from hitting a pothole, which told me that the trailer (body) was too heavy for the frame.
Bringing it home 300+ miles was quite an experience, it would start to resonate, and I'd slow, or pick up speed to get it to stop...
I replaced the 2000# (badly bent) torsion axle with a 3500# leaf spring axle.
That cured 75% of the shimmy.
Today, after studying it for a while, I welded two 2 x 3 x 1/8" tubes to either side of the original tongue, and to the front and second cross member.
The shimmy problem is completely gone.








I agree that the 30" is pretty short, after we get back from our trip, I may add an extension to the next cross member, or just remove all of it and install an A frame or composite tongue that extends back to the 3rd cross member.
I'll keep a close eye on the cross member in question...

Thank you for all your effort and time in replying, it is appreciated!

Rob

[72FJ40]

Based on my experience with trailers, your attachment of the center sq tube is good. Going to second cross member is good; no need to extend to another cross member. And having the tongue below main frame is good; plenty of weld surface. I do not think adding the other tubes in sandwich with or parallel to original tongue will give the strength you are wanting. Use the same sq tube as original tongue and create an A frame brace from approx 12 to 15" behind ball (just in front of the jack) to corner of main frame. Notch and bend the piece being added so that it will extend under the main frame for at least a foot. A butt weld at corner alone places too much stress on the weld. Angle will work for the two added pieces of the A, but I have never been a fan of angle; sq is much stronger even when a thinner wall thickness is used.

[48Rob]

72,

Thanks!

I didn't build the trailer; I'm just getting it in shape for camping.
I've already installed the parallel tubes, and they have corrected the vertical and horizontal movement of the tongue.
We're doing a 300+ mile trip next week, so it will be a good test to see if we need to add an a frame.

Rob