They are made to help level and keep the truck from bottoming out with a load. They install between the frame and leafs. For instance I would keep about 8 lbs psi in them at all times and would never bottom out. Also they allow you to adjust height of the truck slightly. With your typical 4/7 drop the rear will sit lower than the front. Put a few pounds in the bags and now you sit level. They are like 300 to 350 dollars for the kit But unless you want to do a c-notch it is the best option.