I know diddely about 5th wheels, but I am hoping that I will need to soon.
I've seen them mounted behind the rear axle, on top of the rear axle and in front of the rear axle. I'm also handicapped by an engineering degree.
It seems to me that the mount should be 1/3 of the wheelbase forward of the rear axle, since there are two wheels on the front and four in back.
But that doesn't take into account the static center of gravity of the truck. I suspect that, because of the weight of the cab and drive train, an unloaded truck has about 60% of it's weight on the front wheels.
I would also think that, ideally, you would want the center of gravity of the loaded truck where you would have 33% of the weight on the front, and 66% on the rear. (Duallies on the rear. 50/50 otherwise.) My reasoning is that this puts a reasonable amount of weight on the front wheels for steering, and a reasonable weight on the rear wheels for load carrying and braking.
I've also seen some sliding 5th wheel mounts. These would seem to be great for fine tuning.
My next question is about goosenecks. I asked a bed manufacturer about fifth wheel placement and he said it didn't really matter because you can get trailers with goosenecks any length you want. Is that true?
So what do you think?
