Fender skirts are the pieces of body panels which cover the upper portions of the rear tires of an automobile. They were typically detachable to allow for tire changes. They were implemented for both aesthetic and aerodynamic reasons. Rather than air flowing into and being trapped in the rear wheel well, these allowed the air to flow smoothly over the body. A set of these NOS FoxCraft Fender Skirts for a 1958 Impala can start off at $3,500, and have been sold up to $5,000.