What size mud flaps do I need? Have you ever asked yourself or someone else that question? We often get asked how long Gatorback flaps will hang down from the fender and what size one should get based on their truck. So as with most aspects of trucks, each one is different and so is the length from the fender to the end of the flap. Because this is the case, we have put together a table to help you find which size of mud flaps are best for you!