What component in a gear drive system does not affect the speed or torque output of the driven gear?

• A. Driving gear
• B. Output gear
• C. Pinion gear
• D. Idler gear

Answer: (D)

In a gear train, the speed and torque of the driven gear are determined by the gear ratio between the driving gear and the driven gear. An idler gear sits between them to change the rotation direction and adjust spacing, but it does not alter that ratio. So, the driven gear ends up with the same speed reduction or torque increase dictated by the sizes of the driving gear and the driven gear, regardless of the idler’s size. For example, if the driver has 20 teeth and the driven has 40 teeth, the driven gear runs at half the driver’s speed, no matter what the idler between them is. The idler’s role is mainly direction change and layout, not changing the output values (aside from minor efficiency losses due to friction).