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Thread: travel trailer rear hitch

  1. #1

    travel trailer rear hitch

    I want to put a rear hitch on a 4000# 23' tandem axle travel trailer, 16' from cl of wheels to front trailer ball hitch, rear ball would would be 7' 6" from cl of trailer wheels. tongue weight of boat trailer is 230#. boat trailer cl axle to ball is 16' boat & trailer weight 2000 #, truck ball is 5' from cl truck axle. Can someone help me with the numbers to calculate the forces of loads on the trailer and truck? will be using equlizer hitch. Thanks bill

  2. #2
    Administrator Kelly Bramble's Avatar
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    So, you want to put a trailer behind a trailer? Not a simple answers or task.

    You will need to evaluate and likely upgrade the trailer you adding the hitch to. Can you post pictures or a free body diagram?

  3. #3
    Quote Originally Posted by Kelly Bramble View Post
    So, you want to put a trailer behind a trailer? Not a simple answers or task.

    You will need to evaluate and likely upgrade the trailer you adding the hitch to. Can you post pictures or a free body diagram?


    Thanks for the reply Kelly you are correct on the trailer upgrade that is no problem, what I need is help doing the math to figure my weight gain and loss on the various axles when I have it all hooked up. I know there is a formula for figuring out the weight distribution I just dont know how to figure it. Thanks bill

  4. #4
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    In general I think this a simpler calculation than it appears except that I am unfamiliar with an "equalizer hitch" so can you give me more information on that device. Also, what is the current tongue loading of the travel trailer?

  5. #5
    Quote Originally Posted by JAlberts View Post
    In general I think this a simpler calculation than it appears except that I am unfamiliar with an "equalizer hitch" so can you give me more information on that device. Also, what is the current tongue loading of the travel trailer?

    Sorry about that, it would help. tongue weight is 560#. Truck weighs 5600#. with 168" wheelbase. The equalizer hitch distributes the weight between a trailer and the tow vehicle by means of steel bars.

  6. #6
    Technical Fellow jboggs's Avatar
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    This whole has been discussion is about vertical forces, and that is worthy. But all I can see is horizontal instability. Any small "wiggle" in the first trailer would only be amplified in the second. It's easy for me to visualize some "harmonic" speed at which this whole assembly would be virtually uncontrollable, and extremely dangerous. I know UPS and other trucking lines use multiple trailers, but something tells me the big difference is that they have a front and rear axle under each trailer.

  7. #7
    Quote Originally Posted by jboggs View Post
    This whole has been discussion is about vertical forces, and that is worthy. But all I can see is horizontal instability. Any small "wiggle" in the first trailer would only be amplified in the second. It's easy for me to visualize some "harmonic" speed at which this whole assembly would be virtually uncontrollable, and extremely dangerous. I know UPS and other trucking lines use multiple trailers, but something tells me the big difference is that they have a front and rear axle under each trailer.

    Thanks for your response, that's why I would like to know the numbers for proper weight distribution so I can keep the tongue weights in the 10 to 15 % range to prevent the"wiggle" you mentioned.

  8. #8
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    OK, now we have all of the vertical force elements; but before I give more information I think the issue raised by jboggs is an important one to consider so my next question is whether or not you have seen an existing successful arrangement similar to what you are planning and have discussed your plans with people knowledgeable on this arrangement.Now back to your original question. If you were using a standard ball hitch on the boat trailer connection the tongue weight on your truck hitch would be reduced by 230*7'6"/16' = 108 lbs. to 560-108 = 452 lbs. and wheel loading on the travel trailer is currently 4000-560= 3440 lbs. and it would be increased to 3440+230= 3670 lbs. On the other hand, if you use an equalizer hitch on the boat trailer connection and these units work as described in their literature then the truck hitch tongue weight will be increased by 230/2 = 115 lbs. to 560+115= 675 lbs. and the travel trailer axle weight will be 3440+115= 3555 lbs. but to be safe just assume the travel trailer axle weight will be 3670 lbs. The boat trailer tongue weight on the travel trailer connection will obviously simply be 230 lbs.

  9. #9
    Technical Fellow jboggs's Avatar
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    How do you know that keeping the tongue weights in that range prevents instability? That relationship isn't obvious to me. One is vertical, the other is horizontal. Do you have some data to back that up?

  10. #10
    Quote Originally Posted by jboggs View Post
    How do you know that keeping the tongue weights in that range prevents instability? That relationship isn't obvious to me. One is vertical, the other is horizontal. Do you have some data to back that up?
    Im no Engineer thats why Im asking for help with the math so I know what the weights will be. There should be no horizontal forces but the wind. I have been pulling trailers for 40 + years from small utility trailers to tri axle lowboys with over 130,000 # the weight distribution is critical on all trailers to get them to pull straight. Too much either forward or behind axle will cause "bull hunching'' OR " Wig wag". thanks bill

  11. #11
    Technical Fellow jboggs's Avatar
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    "40 + years" That much experience counts for a lot of engineering. I bow to your experience.

  12. #12
    Quote Originally Posted by jboggs View Post
    "40 + years" That much experience counts for a lot of engineering. I bow to your experience.

    Well thanks but experience does not always out weigh science, I have people who work for me that have many years experience and still do things the wrong way. Any help on the math part? bill

  13. #13
    Lead Engineer Cake of Doom's Avatar
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    How is the load to be applied to the trailer(s)?

    I think I'm having a thick day but I'm having trouble visualising this. As mentioned by Kelly earlier: could you provide a sketch/photo/free body diagram please?

    I lifted this from the net as a quick template. Once you can see what forces are going where, it becomes a lot easier to figure out what to calculate.
    weight_distribution2.gif

  14. #14
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    Just a quick note. I provided the requested information earlier today based upon my understanding of the problem but it appears to be tied up in the moderator review process.

  15. #15
    Quote Originally Posted by Cake of Doom View Post
    How is the load to be applied to the trailer(s)?

    I think I'm having a thick day but I'm having trouble visualising this. As mentioned by Kelly earlier: could you provide a sketch/photo/free body diagram please?

    I lifted this from the net as a quick template. Once you can see what forces are going where, it becomes a lot easier to figure out what to calculate.
    weight_distribution2.gif
    Just as the template drawing shows but I have a boat trailer hitched to the rear of the Travel Trailer. Thanks

  16. #16
    Thanks maybe it will appear soon. bill

  17. #17
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    Bill, my post is now entered. Look at the above 09-23-2013, 10:01 AM entry.

  18. #18
    Thanks I submitted a rough drawing maybe this will help.

  19. #19
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    Bill, based upon the diagram you submitted, the tongue weight on the truck will be reduced to the 452 lbs (with the equalizer bar this will be divided evenly between the trucks rear and front axles and the travel trailer total axle loading will be 3670 lbs. again divided evenly between the tandem axles.

    Let me know if this is the information you are looking for. If not, I will give you a call at the number you entered.
    Last edited by JAlberts; 09-24-2013 at 12:19 PM.

  20. #20
    Yes thank you for your help I just wanted to see what my loads, would be. thanks again bill. gone to the lake! DSCN1324.jpg
    Last edited by bsosebee; 09-26-2013 at 04:17 PM. Reason: add photo

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