On normal motorcycles the crankshaft rotates in the same direction as the wheels. In contrast, in MotoGP the counter-rotating crankshaft rotates in the opposite direction. The Ducati engine specialists have borrowed this technical solution from the racing models for the same reasons it was applied in the competitive world. In fact, this solution has advantages related to two aspects of physics: the gyroscopic effect and inertia. The counter-rotating crankshaft makes it possible to compensate part of the gyroscopic effect produced by the wheels while riding, and this results in improved handling and a motorcycle that is more agile when changing direction.
The second advantage is related to inertia (that is, the tendency of an object to oppose a change in state) both of the vehicle and the rotating engine parts. During acceleration, the driving torque transmitted to the ground pushes the vehicle, which reacts by generating a tendency to do a wheelie. Due to inertia, the counter-rotating crankshaft generates a torque in the opposite direction, which thus tends to lower the front end thereby reducing the wheelie phenomenon, with also benefits acceleration.
Likewise, during braking or fast decelerations, the motorcycle experiences a reaction that tends towards rear lift-up, but the crankshaft also undergoes a deceleration (reduced rpms) and this results in an inertial torque in the opposite direction that counters the force seeking to lift the rear end. Consequently, both in acceleration and braking, the adoption of the counter-rotating shaft provides positive effects.
Clearly, this layout requires an additional toothed wheel, the so-called idle wheel (*), which is necessary to transfer the crankshaft motion to the gearbox and then to the wheels so as to provide the correct rotation for the direction of travel.