Motorcycle transmission

Fully-automatic transmissions are far less common on motorcycles than manuals, and are mostly found only on motor scooters, mopeds, underbones, minibikes, and some custom cruisers and exotic sports bikes.

They function in the same way as a conventional fully-manual motorcycle with a sequential gearbox, except they utilize a fully-automatic clutch system, or sometimes torque converter, but still require the rider's input to manually actuate change gears.

An ECU works in conjunction with a sensor and a microcontroller (CPU) to cut the ignition and/or fuel injection momentarily, so the rider can switch gears.

The weight of the largest touring motorcycles (sometimes in excess of 360 kg or 800 lbs) is sometimes such that they cannot effectively be pushed backwards by a seated rider, and they are fitted with a reverse gear as standard.

To avoid accidental operation, the reverse is often engaged using an entirely separate control switch - e.g., a pull-toggle at the head of the fuel tank - when the main gearshift is in neutral.

In earlier times (pre-WWII), hand-operated gear changes were common, with a lever provided to the side of the fuel tank (above the rider's leg).

A lever on the handlebar exploits mechanical advantage through a cable or hydraulic arrangement to release the clutch spring(s), allowing the engine to freewheel with respect to the transmission.

The effective "bite point" is found automatically by equilibrium where the power being transmitted through the (still-slipping) clutch is equal to what the engine can provide.

Below the lock-up point, partially or fully releasing the throttle can lead to the RPM falling off rapidly, thanks to the feedback loop of lower engine speed meaning less friction pressure.

Most modern 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".