How to Efficiently Change Gears on a 21 Speed Mountain Bike
To change gears on a 21 speed mountain bike, start by pedaling the bike and then use your left hand to shift the front derailleur to the desired gear. Use your right hand to shift the rear derailleur to the appropriate gear. The larger gears are harder to pedal but offer more speed, while the smaller gears are easier to pedal but provide less speed. Make sure to adjust your gears based on the terrain and incline you are riding on for optimal performance.