Ron,
The excess weight the WD hitch is distributing is part of the tongue weight plus added weight in the back of the truck. It certainly doesn't reduce the tongue weight. In any case, tongue weight per se isn't what we seek. The tongue weight as a proportion of the total trailer weight is just an analog for the distance the longitudinal center of gravity (LCG) is forward of the pivot point (wheels). The farther forward we get the LCG the more stable the trailer is, other things remaining equal.
Here's how I describe the weight distributing hitch....
Ron and I hitch up his trailer. The rear of the truck sits way low, the front is way high, and the front wheels don't steer or brake worth a darn 'cuz of this.
We stick a long pry bar into the back end of his truck frame and pull up hard. The rear rises and the front drops. I have Ron trot along holding that bar up as I drive...the truck drives really well now, but Ron is getting tired. He chains the bar to the trailer tongue so he can take a breather. This works OK on the straights, but is a big problem on curves. We figure out a pivot system for the point the bar attaches to the truck. It turns well, but is really bumpy. Ron's Mrs. says to use spring steel bars. Duh!...Why didn't we think of that? Ron and I, and his Mrs., just invented the weight distributing hitch.
Ken
