If the driver speed is 800 RPM for a 4-tooth driver and 16-tooth driven gear, the driven speed is ______ RPM.

• A. 800
• B. 400
• C. 200
• D. 100

Answer: (C)

Gear ratio determines how the speed of the driven gear changes when two gears mesh. The driven gear will rotate more slowly if it has more teeth than the driver, and the speed reduction equals the ratio of driven teeth to driver teeth. In this case, the driven gear has four times as many teeth as the driver (16 vs 4), giving a 4:1 reduction. So the driven speed is the driver speed divided by 4: 800 RPM ÷ 4 = 200 RPM. Under ideal conditions, the torque on the driven gear increases by the same factor, fourfold. The other numbers would arise from different tooth counts: no reduction would keep the speed at 800 RPM; a 2:1 reduction would yield 400 RPM; an 8:1 reduction would yield 100 RPM.