Re: Can I tow a fifth wheel trailer with a goose neck hitch?
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Now, take the same trailer, and add an 18" (1.5 foot) goosneck extension, and here is what you get with the same 8,000 pound force.
8,000 lbs(1.5 feet) = 12,000 foot-pounds of torque. That is over twice the designed torque or bending moment rating of the trailer frame!!!!
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You guys must be hanging your trailers and trucks from helicopters. I don't think an 8000 pound trailer puts 8000 lbs of torque on a truck. I can push a pickup on level ground. Does that mean I'm putting out 6000 pounds of torque?
I agree with your concepts and they are all true. I just don't think the numbers are quite a large as you say.
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This may be true, the forces would never be that great, but your missing the point, it is not the numbers that are important, it is the fact that you will overstress your trailer frame by over two times the designed stress of the trailer.
And yes, you may have towed your trailer for tens of thousands of miles with an extension on it without any trouble. Good thing it was designed to be stouter than it needed to be, or you would have broken it by now.
BTW, 8,000 pounds of force is not unheard of at the pin, here is why... Force equals mass times acceleration. So if you have an 8,000 pound trailer traveling at 60 MPH, and you slam on the breaks, giving a deceleration of 5 mph per second (12 seconds to fully stop) then your force at the pin is 8,000lbs(-5 mph/sec), or -40,000 lbs (negative force just means pushing forward instead of backward)total ove rthe 12 seconds, divide by 12 seconds, and you get a force of 3,333 pounds at the pin. Multiply that by 1.5 feet on your 5th wheel extension, to get leverage, and you have 5,000 foot pounds, which is the design load of your trailer, if you reference the last post... This is over a relatively leisurely stop, so a harder stop would be bad...
To the man that has tens of thousands of miles towing with this setup, you are probably okay. 25% FOS on a design load is common in buildings, but i am guessing a dynamic situation like a trailer has a 150% or even 200% design FOS. So you could probably be fine, but if your trailer has a weak weld, or a defect that wouldn't otherwise be a problem, a gooseneck extension could put it over the edge. It is your choice, just make sure you know that you are putting additional stresses in your rig that it was not designed to handle. Do not fall for the fallacy that has been stated here that it is an "apples to apples" comparison.
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