What is sprocket?
Sprocket is a simple mechanical wheel with teeth or small notches which are designed to rotate and engage with the links of a chain or belt. To be compatible, though, they both need to have the same thickness and pitch.
Calculating the sprocket ratio :
This is the number of teeth on the driving sprocket divided by the number of teeth on the driven sprocket.
Example: Front sprocket on has 10 teeth and the rear sprocket has 30, the sprocket ratio is 10/30 = 1/3 = 1:3 or 3