bogies

A bogie is a wheel-assembly under a vehicle that supports its weight, allows steering through curves, and carries suspension and braking elements. The term is most commonly used in rail transport, particularly in British English, where rolling stock sits on paired wheelsets mounted on a bogie frame. The bogie enables even load distribution, smoother ride, and reduced track wear by allowing independent rotation of the wheelsets.

Railway bogies are the wheel assemblies that support most rail vehicles. A bogie has a frame, two or more wheelsets (each with axle and wheels), and suspension between the frame and axleboxes. Primary suspension controls wheel motion; secondary suspension cushions overall ride. Brakes are usually fitted to the bogie, and some bogies carry traction motors for powered vehicles.

Two-axle bogies are common on freight cars; passenger cars often use three-axle bogies or articulated arrangements. Some bogies are powered (drive bogies) with traction motors and gearing; others are unpowered (trailing bogies). Bogies may include dynamic braking parts or be designed to reduce hunting motion, the tendency of wheels to oscillate at certain speeds.

In aviation, a bogie describes the wheel assembly for retractable landing gear. A bogie may carry two or more wheels on a common axle or on separate axles, and it can pivot to align with the runways on touchdown. Some aircraft have twin- or quadruple-wheel bogies, with hydraulic retraction and compression damping; the bogie is attached to the landing gear leg.

On tracked vehicles and heavy equipment, bogies refer to wheel assemblies that support the track or running gear, helping distribute load and provide suspension over uneven terrain.