Most small cars will have kayak roof racks designed for them. Of course, the question of whether you can mount a boat on a small car will also depend on how big the boat you intend to mount is. It goes without saying that the smaller the vehicle and the bigger the boat being mounted, the more difficult the mounting process will be. Some really diminutive vehicles might require a custom-built roof rack that can accommodate a kayak. Of course, there are many kayak roof racks designed for subcompact vehicles, and the best thing to do is to check with the manufacturer for the proper roof rack.