Forgive my ignorance of the proper terms. I may be using “leverage”, “lever”, and “cantilever load” incorrectly.



Description:



This concerns a gooseneck hitch connection in an F350 long-bed pickup.



The gooseneck receiver hitch is properly attached to the vehicle and located ~3 inches forward of the rear axle. If I connected the gooseneck trailer to the hitch as designed the weight on the hitch would be directly above the hitch and be 2,500 pounds.



However, for certain reasons I must move the gooseneck trailer connection point rearward 20 inches. The hitch itself (attached to the vehicle) will remain in its properly located position. I will build a hitch extension that displaces the hitch load point rearward 20 inches. This extension will not be in contact at any point other than to the hitch itself and the trailer when connected. So, I am moving the 2,500 pound load from directly above the hitch to 20 inches rearward of the hitch.



So, what I need is the formula to calculate what the load on the hitch will be when the load is displaced rearward 20 inches. Is it simply 1.67 times 2,500 pounds which would be 4,166 pounds? (20/12*2500)



Also, I realize there will now be a ‘twisting’ force on the hitch itself. Is that twisting force equal to the new load? How would I calculate this twisting force?



Also, what is the correct terminology to properly describe my problem? This 20 inch extension is a sort of lever. And also this hitch extension acts like a cantilever beam of sorts. I’ve looked and looked for the proper terms to describe my problem, but as yet I am unsure what is correct.



Thanks to anyone that sheds light on my problem.

 

 

 

I am pretty sure I figured it out.

The weight doesn't change. The tongue weight is 2,500 lbs on the vehicle, no matter where it is placed on the vehicle.

What changes is the twisting force experienced by the hitch itself. I think that force must be somewhere around 4,200 lbs. But if anyone could shed any light, it would be welcomed.

 

Without breaking out the math, 20" seems like a looonnngggg way off of the normal hitch configuration. That's going to unload the front axle some and make the rear squat.

 

In my mind, since the extension only touches the hitch itself and the trailer connection, the load remains on the hitch (B&W Turnover Ball in this instance). In other words, this extension does not touch the bed of the pickup at any point.

So, this being the case, the weight distribution between the front and rear axles would remain constant (Assuming a stationary, non-moving scenario).

However, there would apparently be a twisting load on the hitch.

 

By offsetting the location of where the trailer's pin weight falls, it matters.

It's like trying to get a stuck nut off with a 3" socket wrench. Break out the 20" breaker bar and there's a whole lot more torque being applied to the nut.

 

I’m no help with the math but I’m very curious about the “extension”. Is this a separate piece that’s going to go between the goose ball in the truck bed and the trailers gooseneck hitch? Or is it somehow attached to the truck at the ball location? Or is it attached to the trailer? Either way how will it be kept stable and not pivot? At which point will it allow for rotation, at the truckbed ball or trailer hitch? And what’s keeping it from rotating at the other connection point?
what’s the “certain reasons” that is requiring this relocation?

 

All good questions.

I am ferrying this trailer (empty) and have other cargo that is against the cab. If I don't temporarily move the hitch position it will interfere with the other cargo.

I could make two trips, and still may. But it is a 1,500 mile round trip, so I'd like to do it in one. That's why I am considering building the extension. This is not a permanent solution, just a one way temporary one.

My hitch is a B&W Turn Over Ball. So the socket for the ball is 2-1/2" square. So I'll remove the goose ball and insert a piece of solid 2-1/2" x 2-1/2" steel bar stock there, so no pivot at the hitch itself. The other end of the extension will have the 2-5/16 standard gooseneck ball. So, only a pivot in one point.

I'll add a drawing incase this is not clear.

 

 

Except where it enters the hitch, the extension will not touch the floor of the pickup bed.

 

I understand what you're planning to create. It's still a lever. If my limited understanding of the math is correct and ignoring the weight of the extension, you're applying about 1.6 lb ft of torque on the socket in the bed when applying 1 lb of downward force on the end of the extension.

 

Yes. That's exactly how I see it. It will be a 'twisting' force on the hitch itself. I have that force at 4,166 lbs. It helps me to see you came up with the same thing. Thanks. Because I am not a 100% sure about it. I am trying to use a common sense approach, since I am not sure about which math to use either.

I posted this to another board of "experts", they say it is effectively moving the trailer axles rearward (which that much is obvious). And since the axles are more rearward that it will lessen the amount of weight on the vehicle. But another "expert" on the same forum says it will increase the weight.

I think both of these "experts" are wrong. The downward force is 2,500 lbs. The hitch doesn't change that as far as I see it.

***This "expert's" forum is a physics undergraduate and post graduate collegiate level forum where they bounce homework questions to each other. They also allow people like us to ask physics questions. I really thought this was a simple question. But it stirred up all sorts of stuff on that other forum. I guess it turns out that it's not all that simple.

 

Here is my logic (assuming a non-moving stationary vehicle):

If we took a 2,500 lb weight, it would not matter where we placed that weight on the chassis. It will always be a force of 2,500 lbs.

The weight of the trailer is the same. I am not changing a single thing in the trailer itself. The trailer's weight at the hitch is 2,500 lbs.

As I see it, the extension is a lever, and that lever is applying a twisting moment to the hitch itself, But that does not increase the weight that the chassis experiences.

Since there is some debate on the other forum (most say that the chassis will experience a 150 lb increased load), I have decided I am going to build the extension and use a certified truck scale to see what is up!

But in my mind, a 150 lb increased load is mostly negligible.

 

The trailer's weight at the trailer's PIN is always 2,500 lbs.

The effect of the extension on the weight carried by the truck increases because the extension is a lever. Beyond the increased weight carried by the tow vehicle, you're also going to see more weight put on the rear axle of the tow vehicle and less weight on the front axle of the tow vehicle because of the lever's action.

By moving the trailer back from where it would normally attach, your breakaway chains may no longer reach.