A two-wheel drive motorcycle is a motorcycle that is capable of diverting engine power to both wheels at the same time. Most motorcycles only divert engine power to the back wheel, similarly to how most bicycle chains only connect the pedals to the back wheel to generate motion.
On a motorcycle, an apparatus called the drive train connects the engine to the wheel or wheels, converting the motion in the engine to motion of the entire vehicle. Two-wheel drive motorcycles use either a more complicated drive train or a system of hydraulics to power both the front wheel and the back. Powering the front wheel improves traction and thereby off-road performance. However, they require more engine power overall, and many designs are heavier than comparable standard motorcycles.