Gear ratio: A small gear with 20 teeth connects to a large gear with 60 teeth. The shaft connected to the larger gear will ____________.

• A. Turn faster and have greater torque.
• B. Turn slower and have greater torque.
• C. Turn slower and have less torque.
• D. Turn faster and have less torque.

Answer: (B)

When a smaller driving gear engages a larger driven gear, the larger gear must rotate more slowly but can deliver more torque. The gear ratio is driven teeth divided by driver teeth, so here 60 divided by 20 equals 3. That means the output shaft (on the larger gear) turns at about one-third the speed of the input shaft. Power tends to stay roughly the same (ignoring losses), so the torque on the output increases by the same factor, about three times. In short, the shaft connected to the larger gear turns slower and with greater torque.