How Strong Does My Tongue Need To Be? (Mark 2)

Ask questions about Harbor Freight trailers, or questions about building your own...

Postby angib » Tue Apr 11, 2006 5:42 pm

Cary Winch wrote:I do still need to point out that people need to realize that the load this chart calculates is the weight at the joint of the tongue to the rest of the frame not the total weight of the trailer.

No, the weights in the chart above are the maximum weight of the whole trailer, if the tongue is to pass the Aussie rule - that rule says the tongue must withstand a load on the coupler equal to half the total trailer weight.

I can well understand if you want to say that that is too strict a rule, particularly for trailers with reasonable tongue weights. I think it is too strict - and the fact that Camp-Inns don't have any problems with their tongues is one of the things that makes me believe this!

However, it's a simple rule that is unlikely to get a home builder into trouble, even if they get an excessive tongue weight, so I think it's useful.

Andrew
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Postby asianflava » Tue Apr 11, 2006 5:45 pm

Maybe we should investigate the Little Guys that had to be recalled due to problems with the tongue cracking/breaking. The construction was obviously bordering on being too light.
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Postby Cary Winch » Wed Apr 12, 2006 9:13 am

Andrew,

I figured you saw the same thing I did to. I tend to try and read the intent of the rule first, too many years trying to interpret UL rules in a previous life.

I completely agree that the chart makes for a great resource for anyone building a trailer. I wish I would have seen something like that years ago.

Most people don't really know the weights of the trailer at different locations while building it, especially if they are first building the frame and havn't cut any wood yet. That is where some generalization is very helpfull. If they can estimate the total weight of the trailer they can use the chart and have a very safe (if over built) frame. If they are more comfortable doing weights and balance calculations they could figure the trailers weight at a more forward position near the front of the body. This would give them a lighter frame using this chart. Since most teardops focus the weight over the axle as much as possible this might be a simple matter of subtracting out everything straight above the axle and either adding or substracting what is fore or aft of it.

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Postby angib » Fri Apr 14, 2006 8:54 am

Harvey ('nobody') was kind enough to measure up his HF 1800lb trailer in detail, so I thought I would post what tongue strength that achieves.

A-frame tongue section: 2.25"H x 1.5"W x 0.12"th x 0.375"lip
Vertical modulus (one section): 0.477 in3
Vertical modulus (whole A-frame): 0.955 in3
Max bending stress, open section: 26,250 psi
Vertical capacity: 25,060 lb-in
Tongue length: 41 in
Max trailer weight: 1,220 lb

That 1,220 lb trailer weight allowed by the Aussie rules is less than 60% of the HF trailer's GVWR of about 2,150 lb (1,800 lb capacity + ~350 lb unladen weight). So that's another suggestion that the Aussie rules are rather strict!

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