I am not sure the exact room under the shelf. You can stack a front and rear tire on top of each other under the plywood. I want to make just two shelves out of metal on the sides of the bed that extend out enough for the wheels of the kart to sit on. Then eliminate anything going across the bed in the middle. Right now this works great since the only thing I have to do to the kart to load it is remove the front nose cone. Wheels, hubs, rear bumper all stay exactly how they come off the track and that is with me running maximum legal width in the back.