Using this guard is easy. First, remove the front wheel spacer of your 2021 Rieju MR 300 (Racing, Pro, or Ranger). Then, attach the aluminium mounting bracket in its place. After that, fit the plastic guard around the front brake disc and the lower part of the caliper. When riding, make sure the guard is securely attached. For maintenance, regularly check the mounting bracket for any signs of wear or looseness. If the plastic guard gets damaged, you can easily replace it. Keep it clean by washing it with mild soap and water after each ride, and store it in a dry place when not in use.