Most manual transmission two-wheelers use a sequential gearbox. Most modern motorcycles (except scooters) change gears (of which they increasingly have five or six) by foot lever. On a typical motorcycle either first or second gear can be directly selected from neutral, but higher gears may only be accessed in order – it is not possible to shift from second gear to fourth gear without shifting through third gear. A five-speed of this configuration would be known as “one down, four up” because of the placement of the gears with relation to neutral, though some motorcycle gearboxes and/or shift mechanisms can be reversed so that a “one up, four down” shifting pattern can be used. Neutral is to be found “half a click” away from first and second gears, so shifting directly between the two gears can be made in a single movement.
In many modern designs, the engine sits in front of the gearbox. From a sprocket on one side of the crankshaft, a chain or sprocket directly mounted to the clutch will drive the clutch, which can often be found behind a large circular cover on one side of the gearbox. The clutch is connected to the gearbox input shaft. For motorcycles with chain drive, the gearbox output shaft is typically connected to the sprocket which drives the final drive chain.
Most manual motorcycle gearboxes have “constant mesh” gears which are always mated but may rotate freely on a shaft until locked by a toothed sliding collar or “dog clutch”. Since the gears are always rotating and can only be accessed sequentially, synchromesh is not generally needed. To save space, both shafts may contain a mixture of fixed and free-spinning gears, with some gears built into the sliding parts.
