A(n) idler gear is mainly used in a multiple gear drive system to _______________.

• A. Increase speed
• B. Align gears
• C. Change direction of rotation
• D. Decrease torque

Answer: (C)

An idler gear’s main job is to reverse the direction of rotation in a gear train without changing the overall gear ratio. In a multi-gear setup, gears that mesh directly rotate in opposite directions. Placing an idler between the driver and the driven gear makes the final gear rotate in the same direction as the input, a layout constraint often required. Because the idler only transmits motion, it doesn’t alter the speed or torque that result from the driver-to-driven gear sizes—the speed depends on the gear ratio of the first and last gears, not the presence of the idler. So it doesn’t increase speed or decrease torque, and while it can aid in fitting the gears into the available space, its defining function is to change rotation direction.