Oversquare engine (short stroke)

An engine is oversquare (short-stroke) when the cylinder bore is larger than the piston stroke, giving a bore/stroke ratio above 1. When bore and stroke are equal the engine is square; when the stroke is longer it is undersquare (long-stroke).

A short stroke keeps piston speed lower at a given rpm, so the engine can rev higher, and a wide bore leaves room for larger valves. That is why sports bikes and motocross engines are strongly oversquare. Long-stroke engines tend to give strong low-rpm torque and are common in cruisers and classic singles.

Bore and stroke alone do not decide the character; cam timing, intake and exhaust matter as much. The figures are listed in every bike's technical data.