Motorcycle Transmission Basics 101

by Don Kuhlman

To clutch or not to clutch?

Actually, in the case of shifting your motorcycle’s transmission, that should be "de-clutch" or to disengage the clutch between gear changes. As with such controversies as oil, tires, helmet use and other deeply religious aspects of motorcycle ownership, I leave these decisions up to the reader. Instead, I’ll try to give a little insight into how your motorcycle’s gearbox operates. Then you, as the informed consumer, can decide what’s best for your application.

The typical modern motorcycle gearbox or transmission is a "constant mesh" design. The name comes from the fact that all of the gears in the transmission are in constant engagement with one another. This differs from some older designs where the gears slide back and forth on shafts, engaging one another one pair at a time. The gears are arranged so that you have a drive gear, coupled to the engine, and a driven gear coupled to the rear wheel. They are arranged on shafts, the drive gear on the mainshaft and the driven gear on the countershaft. In most cases, the mainshaft is driven directly by the clutch, which in turn has one set of plates connected to the engine and the other set connected to the mainshaft. Most clutches are driven off the engine’s crankshaft by a gearset as well. They may use direct gears or a chain or belt drive. This is called the primary drive.

The countershaft drives the transmission’s output device, typically a U-joint in the case of shaft drive, or a countershaft sprocket if it’s chain or belt drive. This is called the secondary drive.