A one-cylinder engine delivers a push once every 720°, and then nothing for two full turns. It is simple, but it shakes: the torque on the crankshaft goes from a big peak to zero and even to negative, and the piston's up-and-down inertia shakes the whole engine. Big flywheels help, but there is a better cure: more cylinders, firing in turn.

With n cylinders firing evenly, a power stroke begins every 720° / n:

• 1 cylinder: every 720°
• 2 cylinders: every 360°
• 4 cylinders: every 180°
• 6 cylinders: every 120°
• 8 cylinders: every 90°

In an inline-4, one power stroke ends just as the next begins, so the crankshaft always gets a push. The torque ripples much less than in a single cylinder.