For cars that do not have crossbars, they can be purchased and installed at an additional cost. Many of the manufacturers that make ski racks also provide the necessary crossbars that are guaranteed to fit their products. If you do not want to go the extra mile to install crossbars on your vehicle, you can purchase an inflatable ski rack that runs along the inside of your roof. Keep in mind that you will have to roll your windows down slightly to use this type of rack, so it may get a little bit cold and windy in your car during the winter.