New Improved Tongue Strength Page - washes whiter!

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New Improved Tongue Strength Page - washes whiter!

Postby angib » Wed Aug 07, 2013 11:00 am

Looking again at the previous tongue strength page made me realise it was a nightmare - too complex and too much wading through warm treacle to get to a result.

So there is now an improved, simplified tongue strength page with either a spreadsheet to download or, simpler still, a table of tongue sections to choose from.

The new method combines the Australian trailer rules and the Intentional Standard ISO 7641 on tongue strength, so it doesn't exactly match the previous page's results. What it does do is recognise that the Australian rules are too strict for trailers that don't go off-road and so the International Standard has been used for those.

All comments and feedback is welcome.
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Re: New Improved Tongue Strength Page - washes whiter!

Postby Fishingtomatoseed » Wed Aug 07, 2013 11:29 am

Beautiful. Thank you for the information and your time to take care of it.
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Re: New Improved Tongue Strength Page - washes whiter!

Postby alaska teardrop » Wed Aug 07, 2013 12:18 pm

    Hi Andrew,
    I have questions, if I may, because I'm seeing something new to me.
    Why is there a difference in the load capacity of the tongue for trailers with or without brakes?
    From your chart it seems that the load capacity with brakes is about the same as they are when using the Australian formula. But that the capacity is about 50% higher without brakes. International rules? What is the reasoning for the difference?
    Thank you,
    Fred
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Re: New Improved Tongue Strength Page - washes whiter!

Postby KCStudly » Wed Aug 07, 2013 2:43 pm

Trailer brakes create a torque load on the frame that is transmitted through the tongue the same as if adding more weight to the front of the cabin.

The reaction of the trailer frame to the brakes being applied is to try to roll forward around the tire, thus creating leverage that is resisted by the "reaction" load point at the coupler. Big lever.

BTW, great job on this, Angib! :thumbsup: :applause:
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Re: New Improved Tongue Strength Page - washes whiter!

Postby angib » Wed Aug 07, 2013 4:00 pm

I've added an extra bit at the end of the page comparing the three type/use categories. Put very simply:
- Braked On-Road is three-quarters as strong as Off-Road;
- Unbraked On-Road is half as strong as Off-Road.

I agree that the likely explanation of the higher strength required by the international standard for braked trailers is the forward pitch on the trailer when braking which will increase the load on the tongue. I was surprised they think it requires a 50% strength increase, but then I'm not clever enough to write an international standard.

Fred, the Off-Road category uses the Australian trailer rules but I've taken the calculation method and assumptions about material strength from the international standard, so that category has become 'stricter' than it was before. It may now be in the overkill region, but then if someone chooses to use the 'strictest' category, I reckon they may be going to give their trailer a hard time.
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Re: New Improved Tongue Strength Page - washes whiter!

Postby alaska teardrop » Wed Aug 07, 2013 6:50 pm

    Thank you both for your explanations.
    KC, I shouldn't think that nose diving would be much of an issue for a well balanced lightweight trailer. But I suppose that rules must be written to encompass large nose heavy trailers too.
    Andrew, I don't remember reading, but it would seem that the Australian rules are written with the assumption of brakes, because brakes would be legally required on larger trailers.
    Anyway, all the trailers without brakes just got a large increase in allowed load capacity until they hit the legal requirement for brakes.
    :peace: Fred
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Re: New Improved Tongue Strength Page - washes whiter!

Postby KCStudly » Wed Aug 07, 2013 8:45 pm

I think 1g of braking force is a reasonable expectation in the extreme case, so that would essentially double the tongue weight, so 50/ct strength sounds to me like a reasonable, albeit conservative, std. for w/brakes.

:thinking:
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Re: New Improved Tongue Strength Page - washes whiter!

Postby working on it » Wed Aug 07, 2013 8:50 pm

  • Andrew- concerning the composite tongue: can a single beam with an overlying single beam of different cross-section and thickness (main beam is 6ft long of 3x3x.187, with 45" forward of the first crossmember...overlying beam is 27" of 2x3x.125), be considered a true composite? If so, would the L1 and L2 figures be added the same as in diagonally braced composites? And another thing...my tongue is connected to three crossmembers; will that significantly increase the load rating?
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Re: New Improved Tongue Strength Page - washes whiter!

Postby aggie79 » Thu Aug 08, 2013 8:45 am

Andrew,
Thank you again for all your work. Your contributions are very much appreciated.

To anyone on this forum,
I have a question about Andrew's spreadsheet, or more specifically about "zipped" files. I can download the files but can't seem to "find" or "extract" the actual spreadsheet from the zipped files. Could you please provide me with a brief primer.

Sincerely,
Tom
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Re: New Improved Tongue Strength Page - washes whiter!

Postby angib » Thu Aug 08, 2013 10:06 am

Fred, the Australian rules are so severe that I don't think braking loads make any difference. And there is a valid reason for this, as they have so many washboard dirt roads which are the perfect place to 'grow' a fatigue crack in a trailer tongue until it snaps.

working-on-it, you don't have stacked tubes on your tongue! What matters is the tongue that sticks forward of the main frame and you have only one tube that does that, so that one must pass the strength test on its own. The rest of your frame provides ample support to the tongue but it can't make it any stronger - the 'weakest link' is the tongue itself.

Your tongue is 45" long (assuming you measured that from the first cross-member to the coupler ball), so the 3"x3"x3/16" tube is good for a trailer weight of 3300 pounds unbraked on-road and 1600 pounds off-road.

The 'three cross-members' issue is worth addressing on its own. The middle one of the three will be doing almost no good, but the spacing between the first and the third is good - that easily passes the half-tongue-length test I've added to the web page.

In your particular design only (this does not apply to any other trailer), the centreline longitudinal within the main frame - what you have called one of the 'stacked tubes' - provides so much support to the tongue that it doesn't really matter about most of the cross-members.

Tom, when are you getting these ZIP files? None of the current spreadsheets are zipped, so they don't need to be extracted. However they are in Excel 2007 format, which can't be opened by earlier versions of Excel. I don't know if that's your problem, but other folk may get caught by it, so I've added spreadsheet versions saved in Excel 97/03 format.
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Re: New Improved Tongue Strength Page - washes whiter!

Postby aggie79 » Thu Aug 08, 2013 4:23 pm

angib wrote:Tom, when are you getting these ZIP files? None of the current spreadsheets are zipped, so they don't need to be extracted. However they are in Excel 2007 format, which can't be opened by earlier versions of Excel. I don't know if that's your problem, but other folk may get caught by it, so I've added spreadsheet versions saved in Excel 97/03 format.


Thank you, Andrew. I was viewing from my work computer that had an earlier version of MS Excel. I was able to open the 97/03 format.

Sincerely,
Tom
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Re: New Improved Tongue Strength Page - washes whiter!

Postby working on it » Thu Aug 08, 2013 7:53 pm

angib wrote:working-on-it, you don't have stacked tubes on your tongue! What matters is the tongue that sticks forward of the main frame and you have only one tube that does that, so that one must pass the strength test on its own. The rest of your frame provides ample support to the tongue but it can't make it any stronger - the 'weakest link' is the tongue itself.

Your tongue is 45" long (assuming you measured that from the first cross-member to the coupler ball), so the 3"x3"x3/16" tube is good for a trailer weight of 3300 pounds unbraked on-road and 1600 pounds off-road.

The 'three cross-members' issue is worth addressing on its own. The middle one of the three will be doing almost no good, but the spacing between the first and the third is good - that easily passes the half-tongue-length test I've added to the web page.

In your particular design only (this does not apply to any other trailer), the centreline longitudinal within the main frame - what you have called one of the 'stacked tubes' - provides so much support to the tongue that it doesn't really matter about most of the cross-members.

  • Thanks Andrew, for your evaluation. I missed the "half-tongue-length test" until now. About the three cross-members: the first is the 2 x 3 x 1/8 tube (its the added extension for the original trailer frame), the second is c-channel (the original first crossmember), and the third is the original second cross (also angle steel).
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  • That's why we added rectangular tubing for the front and rear extensions (12" front, 24" rear), and added the longitudinal tubing the length of the trailer. My previous thoughts were that the original angle steel crossmembers were only good enough for "locating" the single beam tubing, preventing side play, and that the centerline tubing was the real strength behind the tongue. In a way, then couldn't the entire length of that tubing be almost like having a 45"+100" single beam of 2x3, as a composite added to the 72" of 3x3? Granted, the tubing is welded in segments, but the welds have deep penetration, so its almost a solid run? I am pleased that your evaluation shows the strength of 3300lbs unbraked, and since the rest of the trailer is bolted and glued 3/4" ply, then it shouldn't fall apart (assuming that the spindly axle is strong enough...but that's another story). Thanks.
Last edited by working on it on Sat Aug 05, 2017 7:12 pm, edited 1 time in total.
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    • 27x8.5-14LT tires,
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    • A/C & heat,Optima AGM battery,
    • extended-run 2500w generator,
    • Coleman dual-fuel stove & lantern
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Re: New Improved Tongue Strength Page - washes whiter!

Postby Bogo » Mon Sep 02, 2013 11:56 pm

The Excel 97/03 format looks to work fine with LibreOffice Calc. :thumbsup:

It's telling me I can go to 3x2x1/8" for an locally available A513 steel tube (min 72k psi yield, 87k psi break) or 3x2x3/16" A500 tube (min 46k psi yield, 58k psi break) when I designed using a guesstimated 3x2x1/4" tube. Makes me think I can shave some weight off the rest of the frame.
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Re: New Improved Tongue Strength Page - washes whiter!

Postby alaska teardrop » Sat Jun 21, 2014 11:57 am

    Hi mike,
    Although Andrew's "Tongue Strength" pages are in the Design Library, I think it would also be helpful if this tread where made a 'Sticky' in this section of the forum.
    Thanks, Fred
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