Let me explain what the Mountain Bike Gear Shifting System Components are, before go into details about how to shift gear on Mountain Bike. It is easy to understand how the gear works.

The crank is bolted onto the bottom bracket. It consists of three chainrings. Chain Rings are bolted into the cranks. Usually they come in three size ranges:

• big ring (48-42 teeth)
  
• middle ring (36-32 teeth), 
  
• small or "granny ring" (26-20 teeth)

The "cogs" or "sprockets" could be found in the rear hub. Modern sprockets consist of 7-9 size ranges from 36-11 teeth. Normally, the 7 and 9 speed sprockets have the same heavy and light gear. The difference is in the mid-range gear. The 9-speed sprocket has more mid-range speed which lessens the change in speed upon up or down shift.