For a step-by-step tutorial check out our article on How To Install A Custom Rear Fender. First you need to determine the width of the tire you want the fender to cover. The fender you choose should cover the entire width of the fender, and fit the frame of the bike. Once you have the fender, it is best to mount your tire and wheel on the bike. Lay a folded towel on top of the tire and place the fender in place. Adjust as needed making sure you have plenty of clearance. Next mark and drill your mounting holes. Be sure to wrap tape around your drill bit so you can control the depth. You do not want to drill through your fender into your tire.