Stroke

In an engine, stroke is the distance the piston travels from top dead centre (TDC) to bottom dead centre (BDC), set by the crankshaft throw. Together with the bore (cylinder diameter), it determines the engine's capacity (displacement).

Engines with a short stroke and large bore (oversquare) rev freely and suit high-performance sport bikes. Long-stroke engines (undersquare) usually give strong low-rpm torque, as on many cruisers and big singles. The terms two-stroke and four-stroke refer to how many piston strokes make up one combustion cycle.

The word stroke is also used for the length of a shock absorber's travel, so 'shock stroke' and 'wheel travel' are related but not the same, because of the linkage ratio.