Overdrive gear

A gear ratio below 1:1 is called overdrive: the gearbox output shaft turns faster than the input shaft. In motorcycle gearboxes the top one or two gears are often overdrive ratios, and some touring bikes have a tall sixth gear marketed as overdrive.

The benefit is lower engine speed at motorway pace, which reduces fuel consumption, noise and vibration. The cost is less acceleration in that gear, so overtaking usually needs a downshift.

Note that the overall gearing also depends on the primary drive, sprockets and tyre size, so even in overdrive the rear wheel still turns much slower than the crankshaft. Changing the rear sprocket is the common way to fine-tune cruising revs.