The 2009 Yamaha YZF-R1 gained a 998 cc inline-four engine with a crossplane crankshaft. Developed from the YZR-M1 MotoGP programme, the layout aimed to make drive easier to control, particularly when accelerating out of a corner.
Crankshaft rotation is influenced by combustion and by piston inertia. Pistons accelerate and slow during every stroke; their movement creates torque fluctuations independent of throttle position. Those fluctuations can obscure the rider’s sense of engine response.
The crossplane layout uses 90-degree crank offsets to change how the four pistons’ movements relate to one another. This reduces inertial torque fluctuations and helps produce a more direct throttle response. The point is the character of power delivery, beyond the headline peak-power figure.
Yamaha later used its Crossplane Concept to guide the character of twin- and three-cylinder engines too. The name therefore does not imply identical crankshaft construction across every model: the R1’s specific four-cylinder mechanism should be distinguished from the broader engine-development philosophy.