The correct size depends entirely on what area of the car you’re looking to clean. If you need a good all-rounder, then it may be best to opt for a medium-sized brush head that can work over larger areas without any extra effort from yourself but can also fit into tighter spaces. Of course, smaller brushes will be more effective at getting into those tougher spots, while larger brush sizes will cause your cleaning to be done within minutes. Think about the size of your vehicle and the time you’re willing to spend on cleaning your car before buying your brush, and you’ll be sure to choose the correct size for your needs.