I How Does Moving a Gooseneck Trailer Connection Rearward Affect Hitch Load?

[jrmichler]

My understanding of the problem. The trailer wheels are not moved. The only change is a 20" extension that moves the hitch point 20" farther from the wheels. The load is not changed between the two cases. The total weight of the trailer does not change, except for a small additional weight from the welded extension.

If my understanding listed and shown above is correct, then @Baluncore's calculation in Post #38 and quoted below, is completely correct. Since the total weight does not change, the weight on the wheels will increase by 148 lbs with the 20" extension.

The second part is the unbalanced mass that provides a moment, that rests effectively on the hitch. That moment is 2500 lbs at the old hitch position, 318.5" from the axle-set, which works out at;
318.5" * 2,500 lbs = 796,250 inch⋅pounds
If you extend the trailer axle-set to hitch point length by 20", the length becomes 338.5", so the vertical load on the tractor hitch will become;
796,250 / 338.5 = 2,352 lbs, which is 148 lbs less than the original.

He calculated the tongue load moment in his first calculation. A moment is a force times a distance. In this case, the force is the tongue load in Case 1 and the distance is the distance from the center of the pin to the center of the axle. When you change the distance from the tongue force to the axle, the moment does not change. In his second calculation he takes the same moment and the longer distance, and finds the new tongue load.

I am serious about understanding this. And I am open and willing to be wrong; but I am not willing to misunderstand it.

You have the right attitude. Do not give up, we will get you there. A good experiment to show the concept is to clamp a board to a toy wagon, load the wagon with something heavy, then lift one end of the wagon by lifting the board using a spring scale. The farther from the wagon that you lift, the less the force to lift one end.

My plan is to test our answers by using an actual certified truck scale.

Good plan. Just be aware of the weight of the extension. If the extension adds 150 lbs weight, the new tongue weight will still be 2500 lbs.

 

[A.T.]

Seems like two different things are being discussed:

Current Configuration

Proposed Configuration

For the above modification, the vertical force at the arrow location doesn't change. But you get a moment transmitted where the dark connector attaches to the rest of the truck.

For this modification, the vertical force at the vertical arrow location does change (decreases). But you get a moment transmitted by the extension where it attaches to the trailer (thick front wall).

 

[Lnewqban]

"Two extreme cases:
If all the weight (trailer plus usefull load) could be relocated on those wheels, no weight would be felt by the truck.
If it could be located aft the wheels, the truck would feel a lifting force."

Yes, 100% - Exactly correct.

As far as "but it changes" I think it will not be an appreciable amount. - it will be negligible.

Is it what you have in mind similar to this?

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