If the driven sprocket has 18 teeth and the driver sprocket has 54 teeth, the sprocket ratio is

• A. 0.333
• B. 3
• C. 1
• D. 0.6

Answer: (A)

In a belt or chain drive, the ratio is found by comparing how many teeth are on the driven sprocket to how many are on the driver sprocket. The ratio equals driven teeth divided by driver teeth.

Here, the driven sprocket has 18 teeth and the driver has 54 teeth, so the ratio is 18/54 = 0.333 (approximately 0.333). This tells you the driven sprocket has one-third the teeth of the driver, so the driven will rotate three times for every one turn of the driver. In other words, the driven experiences a three-to-one speedup relative to the driver. If you prefer another way to view it, the driver-to-driven ratio is 3:1.