Metal spur gears are a no no, you want something to fail in your drivetrain so only that breaks. Ive tried the metal one and it broke every single tooth off the spur and the clutch bell. If you mesh the plastic ones right you will have zero problems. And also make sure your not landing jumps on the throttle. Ive avtually stripped a spur going over speed bumps, i was just doing speed runs over them and it stripped from that little of air, and being full throttle.