Bare car roofs, also known as naked roofs, don't have any kind of rail, fixpoint or gutter to have a bar rack to attach to. In order to attach a cross bar system on to the roof, the rack will have to "clamp on" with custom fitted clips between the roof's edge and where the doors shut. Yakima, Thule, and Rhino have all designed bare roof rack towers and hundreds of different clips to make sure there is a fit for virtually all roof lines.