Two or three-axle truck equipped with a central pivot point linking it to the vehicle's chassis beneath which it is mounted. The pivot point enables the bogie to turn as the track curves and can even move sideways. A bogie behaves in the same way as a non-bogie wagon. On a waggon or car, the bogie enables the mass of the vehicle to be increased (since the stress on the track is more evenly distributed). On a locomotive, it helps to improve stability.