FAQ: Gear ratios and sprocket selection

[MattR]

Question:
How do I determine the gear ratio based on my front and rear sprockets?
What sprockets do I use for more torque and better acceleration?
I want more top speed... what sprockets should I change to for road use?

Answer:
The best way to explain gear ratios is to see them in tabular format. As shown below, the same gear ratio can be obtained by several combinations of front and rear sprockets. The gear ratio is calculated by dividing the "rear sprocket number of teeth" by the "front sprocket number of teeth". Lower gear ratios provide more top speed but less torque and acceleration. Whereas, higher gear ratios provide more torque and acceleration but less top speed.

An example is shown below to help interpret the table. It may be seen that a reduction/addition of 1 tooth on the front sprocket is equivalent to approximately 4 teeth on the rear sprocket. It should be noted that smaller front sprockets (such as 12T) can cause more chain wear. While swapping front sprockets may offer convenient setups between road and tight singletrack, this does result in a larger jump. By changing the rear sprocket, fine increments in gear ratio can be obtained with each tooth.