Add-a-Leaf helper springs are one of the oldest and most common ways to increase the weight capacity of a Ford Transit . They are simply a specially formed leaf designed to be inserted right into the existing leaf spring. Add a Leafs are also often one of the only alternatives when adding weight capacity to a vehicle that has an OEM or aftermarket helper spring above the existing leaf spring because they will not take up any room under the chassis, other than the additional thickness of the leaf itself.