Outside Diameter

Outer diameter

The outside diameter is the longest linear distance across a gear. If the driver and follower gears in a two-gear transmission have the same outside diameter, the gears will turn at the same speed, producing no change in torque, whereas differing outside diameters change the turning speed and output force. A larger driver gear turns the smaller follower gear faster, but reduces the output force; a smaller driver gear increases the output force, but reduces the turning speed of the larger follower gear.