Weight Distribution Hitch?
The weight distribution system consists of a special ball mount that slides into your truck's reciever and has mounts beneath the ball mount platform for 2 large spring bars that extend back under the trailer a-frame and connect, via chain links, to 2 clamps that are mounted on the sides of the trailer a-frame. When you connect up the spring bars and pull the clamps tight, then set the trailer down on the hitch ball, the spring bars help carry some of the tongue weight. Because they are stiffly mounted to the truck via the reciever hitch, they transfer some of the tongue weight to the truck's front axle and some back onto the trailer axle too. This is 'distributing' the weight, and helps the truck to stay level with the trailer connected. The weight distribution system also helps keep the truck and trailer from 'porpoising' when crossing dips in the road.
Part of the weight distribution system is also usually included a sway control bar, which is basically a long shock absorber that connects from the ball mount to the trailer a-frame, that dampens side to side movement of the trailer, helping to keep it in line behind the truck instead of wanting to wag around. This is good for high profile trailers like RV's or enclosed cargo trailers where there is alot of surface area for cross-winds and the wind from passing trucks to act on the trailer and cause it to want to sway behind the truck.
For a better explanation of how weight distribution and sway control work and to see pics of these type of hitches, visit the Reese hitch website: www.reese-prod.com, or visit www.etrailer.com.


