Pyörästö

Pyörästö is a term used in Finnish railway technology to refer to the wheelset—the assembly of wheels and axles that provides the rolling interface for rail vehicles. In practice, a pyörästö consists of two or more wheels mounted on one or more axles, with bearings and support components, and it may include braking equipment. Wheelsets are typically mounted in bogies, though some vehicles use non-bogied wheel arrangements.

A typical pyörästö includes two wheels on an axle, axle boxes or bearings, and suspension elements that absorb vertical loads and allow limited lateral and rotational movement. The wheels are usually steel and feature a tread profile designed for wheel-rail contact. In many designs, braking hardware is integrated with the wheelset or attached to the bogie to provide effective stopping power.

The main function of the pyörästö is to transmit propulsion and braking forces between the vehicle and the track while carrying the vehicle’s weight. It must sustain repeated loads under varying speeds and temperatures while guiding the vehicle along rails. Wheel geometry, including conicity and flange design, influences ride quality, wear patterns, and the ability to negotiate curves without excessive flange contact.

Variants and configurations range from simple two-wheel sets to complex multi-axle wheelsets within bogies. Differences arise from intended use, such as passenger versus freight service, high-speed operation, or heavy-haul duty, as well as whether braking is integrated with the wheelset.

Maintenance and safety are central to pyörästö management. Regular inspections assess tread and flange wear, bearing condition, and suspension components; wheels are reprofiled or replaced as needed; defective axles or cracks require removal from service.

See also: Bogie, Wheel profile, Flange, Wheel wear, Rail vehicle maintenance.