The straight-3 employs a crank angle of 120° and is thus rotationally balanced; however, since the three cylinders are offset from each other the firing of the end cylinders induces a rocking motion from end to end. The use of a balancing shaft with counterbalancing weights that work in antiphase to that vibration produces a smoothly running engine.
The straight-3 is the smallest engine in use in modern cars, generally for displacements of 1 litre and under. Cars in the 'super-mini' class often use them on base models, as do the Japanese Keicars.