It requires an understanding of physics specifically related to torque.
But the simple explanation:
with the 5th wheel hitch all the force is applied directly to the pin in a basic forward (or backward when stopping) direction,
but the gooseneck adapter is hanging some distance below the pin. That adapter is essentially a lever with the force applied at the bottom of that lever. And a lever applies a rotational force to whatever it is attached to. And worse, it amplifies that force in a rotational direction rather than straight on direction.
Easiest way to visualize it is to relate it to a cheater bar. You put a short wrench on a tight bolt and it is hard to remove. You put a cheater bar on the wrench and suddenly it is easy to remove, all because of the amplified force (torque) applied to the bolt via the longer lever (cheater bar).
With the gooseneck adapter that amplified rotational force is applied to the pin box and subsequently to the front part of the frame.
the Engineers are right... but the point I'm trying to make is, with an gooseneck adapter and even with the "proper" fifth wheel hitch" the damage done is not at the "pin" or at the hitch. The damage occurs back of the pin and pin box, at the frame. With the porpusing and high speed over rough roads combined with perhaps an overloaded front end of any trailer fifth wheel or gooseneck, the damage occurs mostly at the trailer frame, not at the hitch (unless a roll over or partial roll over where it doesn't matter what hitch your using, there's going to more then trailer frame damage).
Have seen plenty of piled up fifth wheels in heavy transport yards with mounting plates tore/bent, and a number of trailers with the "pin" pulled out of position, due mostly to heavy loads and bad driving habits on poor road conditions. Drive a tractor trailer on ice roads, flying over hummocks (raised rounded mounds of vegetation covered in ice and snow... akin to riding a roller coaster) tell me that doesn't stress the fifth wheel/pin/pin box or tractor/trailer frame. I'd make an educated guess, that most damage if not all to fifth wheel trailers is from the "rough" ride some get and really, little to do with what method is used to tow them.
Ya'll remember those faulty Lippert frames, can't find anything on the failures caused by gooseneck adapters, looks like all the failures were with a "fifth wheel hitch"? Could be wrong, maybe the good people here can post or direct me to factual stories of Gooseneck failures?
