RE: Fin Maintenance
I know 2 moments where you would sand your fins
1. you touched a rock and your fin has some small "problem". Sand it back in shape to avoid spinouts.
2. when your fin is making a whistling-sound on high speeds (like the select production fins). You can sand the back of your fin to get the whistling-sound away. I know also some gps-speeders who sand their fins to get better speeds.