A weight-distributing hitch uses an adjustable spring-bar system under the trailer tongue that joins the trailer to the hitch head and receiver to distribute weight evenly among all axles of the tow vehicle and trailer. It effectively takes the normal center of the weight off the hitch and redistributes it forward to the vehicle axles and back to the trailer axles. Essentially, the spring bars push down on the rear of the trailer tongue, which transfers weight to the trailer axles, and pushes up on the hitch, which transfers more weight from the hitch to the vehicle’s front axle. The result is that the weight is distributed more evenly among all the axles on the truck and trailer. Pretty neat.
A good guideline for weight-distributing hitches is that you should use one if the trailer weighs more than 50-percent of the tow vehicle's weight.
Weight-distributing hitches use conventional Class III (up to 6000 lbs. towing capacity, 350 to 600 lbs. tongue weight) and Class IV receivers (up to 10,000 lbs. towing capacity, tongue weight 600 to 1,000 lbs.), which bolt to the frame and your vehicle and use 2-inch draw bars. These are compatible with pickups and SUVs with sufficient tow ratings. Where weight-distributing systems differ is at the hitch itself. Where conventional hitches use a ball and draw bar, weight distributing hitches use a shank to which the ball mounts and the spring bars of the weight-distributing system attach. Most often the opposite ends of the spring bars attach to the trailer tongue by chains. If you are towing a tall recreational vehicle trailer or an enclosed car trailer, which can get blown around by high crosswinds, consider a sway-control system, which quells side-to-side movement that can be unnerving and dangerous at freeway speeds.
The type of weight-distribution hitch system you need for towing will vary with the weight and size of the trailer. Differences include shank bar length and spring bar length. Most hitch manufacturers sell systems in kit form, but again, it is best to have a professional shop do the calculations for you, perform the work and help familiarize you with how the system operates. Because of the differences in weight-distributing systems, hooking up a weight distributing hitch varies from system to system, so it is best to consult the manufacturer. In general, hook the trailer to the hitch, then link the spring bars to the trailer tongue, then check your lights, turn signals and brakes.