These leaf overload kits are auxiliary leaves which bolt on to existing leaf springs to give a substantial increase in spring rate automatically when the vehicle is loaded. Because they become progressively more active as load is added and less active as load is lessened, they give appropriate support to maintain good, comfortable, stable, & level ride regardless of the load situation. Any pickup, van, or SUV needing overload support but having a suspension, which is not badly sagged or broken, can benefit greatly from a Progressive Leaf Overload Kit. They are easy to install (1hr. to 1 1/2 hr). Note: If the vehicle has existing factory overloads, they must be removed before installing this style kit.