Two-wheel-drive (2WD) denotes vehicles with a drivetrain that allows two wheels to be driven, and receive power and torque from the engine, simultaneously.
For vehicles that have part-time four-wheel drive, the term refers to the mode when 4WD is deactivated and power is applied to only two wheels.
This scheme greatly improves offroad performance, but is quite complicated and requires more power to operate, thus most 2WD machines are either "exotic" bikes for enthusiasts or created with special uses in mind.
This scheme greatly improves offroad performance, but is more complicated and requires more power to operate, thus most 2WD machines are vehicles created with special uses in mind such as trials or military use.
The first use of the sidecar drive appears in 1928 with the apparent independent invention of Baughan in the UK, and Mokharov in the USSR.