Most trailer hitches feature a 2-inch receiver and the weight distribution system can be inserted directly into that. The first part you'll install is called a shank. These usually plug into the receiver and can be turned in an upward or downward direction, due to the fact that when both vehicles are level, one is often lower or higher than the other. A head assembly is mounted onto the shank, and it provides both the platform for the hitch ball and the spring bars. At this point, the trailer can be re-hitched to the towing vehicle.
Once the vehicles are back together, we can continue installing the weight distribution system. In most systems, the setup basically works like this. Spring bars (remember either round bars or trunnion bars) run from the head assembly to a pair of chains. These chains hang down below the trailer from a set of brackets and attach to them in a way that creates tension along the spring bars. As the tongue weight pushes the bars down, the chains pull the bars up. In order to straighten out to their natural positions, the spring bars push up on the head assembly, distributing the weight among the axles.
The next step in the process is usually to attach the chains to the spring bars and insert the bars into the head assembly. Then the brackets are mounted on the trailer and the chains are attached to those, often with a lift lock. The brackets should be lined up with the ends of the bars, and you generally want at least five chain links showing.
There are two main elements to keep in mind during the installation process. The first is the change in the height of the wheel well rims of the two vehicles. You'll want to measure them before, during and after installation to make sure the weight distribution system is spreading the weight evenly and appropriately. The second aspect is the angle of the bars -- they should run parallel to the tongue of the trailer or downwards towards the ground, and often the head assembly can be tilted to accommodate this or the amount of chain links can be adjusted.
Some systems (especially those that also offer enhanced sway control) may use slight variations, such as a pair of L-shaped brackets in place of the chains, but the systems work in similar ways. Just remember that it's a very good idea to get a professional to help you determine what weight distribution system will work best for you, and to follow the instructions carefully while you're installing it. Once you're ready to ride, get lots more great transportation links on the next page.