Hitch load capacity with a load distribution hitch
I find that these equations can be of great help in answering many further questions that arise about the use of Load Distribution hitches. One example is:
“Why is my hitch rated for 5000 pounds, but 10000 pounds with a Load Distributing hitch?”
We have seen, from equation 6, that the TV rear axle is lifted by a force U when the chains are tightened. This uplift is caused by the chain tension lifting the hitch upwards with a force which we will label Z. To calculate Z, take moments about the TV front axle:
U*W=Z(W+H), and hence Z=(U*W)/(W+H) , equation 11, giving the load taken off the hitch when the chains are tightened.
If I input the figures for my rig into this equation, the uplift at the hitch, Z, is calculated at 370 pounds. The original hitch load (the tongue weight) was 800 pounds, so when the chains are tightened, the hitch load is reduced by 370 pounds from 800 pounds to 430 pounds. The load on the welds and bolts of the hitch are almost halved. Now I understand why my hitch capacity doubles when I tension the chains.
Nick.
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Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
Nick, trust me... there's no failing in your explanation. Others have grasped it easily. There are those of us though, me in particular, who just glaze over when the opening paragraph starts with "Train A left the station at.... and train B left travelling in the opposite direction". We're just not wired that way. I will also say that we who are challenged in that fashion are extraordinarily grateful for those of you who have a gift for it, and who can figure this stuff out for us and are willing to share the results!
Roger
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AIR 2053 “A generation which ignores history has no past and no future.” Robert Heinlein 2006 Bigfoot 25B25RQ towed by a 2001 Born Free 23RK moho
Twink, thank you for the kind encouragement. If I've lost you, that's a failing in my explanation.
Nick.
Not really Nick, I'm just too dense. It'll take me several runs for it to click....your info is well posted, just needs to sink into the grey matter in my thick skull.
The attachment to this post shows how the calculator looks. The forum will not permit .xls file extensions, so anyone wishing to use the calculator can e-mail me, and I will send the Excel file. It was created on Office 2003 on a PC and tested on OfficeX on a Mac.
Nick
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Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
What sway control and any add ons would you recommend for a 67 Safari being towed by a 94 Ford f150 4X4 with a 5.0 litre engine. I've got a Drawtite class III with 2" Reese ball. Do you sell sway bars that'll mount and match properly? And do you sell the electrical coupling for connecting the lights, brakes to a contemporary connector?
Having read the above posts, and subsequently passed them through the proprietary Chartered Financial Consultant formulas, it has been determined that the minimum amount of life insurance required for owning a properly fitted weight distribution hitch is $500,000.
Inquire within....
What sway control and any add ons would you recommend for a 67 Safari being towed by a 94 Ford f150 4X4 with a 5.0 litre engine. I've got a Drawtite class III with 2" Reese ball. Do you sell sway bars that'll mount and match properly?
Bill, I assume (probably incorrectly) that you are asking about load distribution bars. if you measure the tongue weight (weigh station or bathroom scales with a lever), and take 3 measurements of your rig (Rear TV overhang, trailer hitch to axle , load bar length) with a tape, you can enter these figures into equation 8 at post 1 to this thread. A few minutes with pencil and paper or calculator will give you the minimum total capacity required for your load bars. You would then buy the next size above that figure in the catalogue. Setting up the system properly is another matter altogether, but that is covered in detail elsewhere.
If that idea doesn't float your boat, I'm sure owners of similar rigs will make recommendations.
Nick
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Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."
I really enjoyed your load distribution analysis. I was wondering if the equations changes if you put an extended hitch on the Dodge truck? I assume it just changes "H" but I want to make sure. I have a '31 that I will be hitching to a Dodge Cummins extended cab with a cab over camper on it and I need to extend the hitch so I can turn without damaging the cabover. Thanks, Frances
After reading your excellent posts on WD hitches, you have brought me back 35 years to Engineering Mechanics class......and other fond memories of that era. Thanks for the work-up and Karma to you! .
Well, in order to grasp this analysis in light of the economic impact of misalignment creating greater lost opportunity costs for the individual member, we should estimate the beta weight as well as the structure coefficients utilizing the simple matrix algebra equation of
(X'X)inverse X'Y.
I really enjoyed your load distribution analysis. I was wondering if the equations changes if you put an extended hitch on the Dodge truck? I assume it just changes "H" but I want to make sure. I have a '31 that I will be hitching to a Dodge Cummins extended cab with a cab over camper on it and I need to extend the hitch so I can turn without damaging the cabover. Thanks, Frances
Frances,
I was hoping Nick would answer, but it looks like he is offline this evening.
The answer to your question is "yes". I would ask, however, that you pay attention the caution Mr. Crowhurst stated earlier:
" . . . . The equations are simple practical tools to assist in the selection of a load distribution hitch. An analogy would be the decision as to which paddle a kayaker should buy. The vendor should give advice based on the height of the paddler, the beam of the kayak, the type of water being traveled. The kayaker should then be equipped with a paddle “fit for purpose”. However, it doesn’t mean she’ll be safe or efficient in the real world situation of moving water. That will require skill, experience and judgment. Just like towing heavy."
It's great that you are working through the math. If you need help, feed me the numbers, I have all the equations loaded onto a spreadsheet.
Be careful about where you let the numbers take you. I have a gut feeling that towing a 31 ft airstream behind a pickup with a cab-over camper might be quite a load. But if it's a nose heavy diesel with a dual axle it might work.
Experience with Dodge diesel. 4dr 2wd short box.
When I got the truck, one week before the airstream arrived, and put the weight dist hitch setup together, I had "help" from the trailer/mech/sales/helper/guy. The truck/trailer package was the worst riding vehicle, other than a forklift, that I had ridden in. Sway, wiggle and bam on the freeway expansion joints.
I repositioned the ball mount 25 miles from the dealership. It got better.
The thing that really helped, weighing the truck when empty, 4200# front axle, 3000# rear axle. Tounge weight 900#. So using the calculations, short box truck, no WD bars needed? I could not believe it, but did a test drive anyway. Just hooking the 1000# WD bars, hand tight. 50# air in all truck tires to match the tire mfg load specs, 45# in the stream tires, no fresh water on board.
Smooth, nice, stable, and fast=== but never over the 65 mph? tire max?
If you want optimum performance, you have to know what it weighs. Weight it first and most of the guess work is gone. Thanks for the calcs.
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It'll take me several runs for it to click....your info is well posted, just needs to sink into the grey matter in my thick skull. 
Yessssss
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