axle

An axle is a central shaft that connects wheels or other rotating components, supporting them and providing a means to transmit torque from a drive mechanism to the wheels. It is a fundamental element in many machines and vehicles, where it may act as a structural member and a rotating shaft at the same time.

In vehicles, axles are classified by how they handle power transmission. A live axle (also called a drive axle) transmits engine torque to the wheels, while a dead axle carries load and provides suspension support but does not drive the wheels. Axles may be solid (rigid) or part of an independent suspension system; a solid axle connects both wheels with a single rigid member, whereas independent arrangements separate wheel mounting to improve ride quality.

Key components associated with axles include bearings and seals to allow smooth rotation, an axle housing to provide support and lubrication, and, on drive axles, a differential or drive gears that distribute torque to the wheels. Modern front-drive vehicles commonly use axle shafts with constant-velocity joints to accommodate steering angles while transmitting torque.

Railway and industrial contexts also use the term axle: a wheelset consists of two wheels mounted on a single axle that rotates as a unit. In machinery, the axle may be a supporting shaft for rotating equipment, transmitting torque from motors or gears.

Common design considerations for axles include strength, stiffness, fatigue resistance, load-carrying capacity, lubrication, and reliability under bending and torsional stresses. Proper maintenance of bearings, seals, and lubrication is essential to reduce wear and prolong service life.