A
train wheel or
rail wheel is a type of
wheel specially designed for use on
rail tracks. A rolling component is typically pressed onto an
axle and mounted directly on a
rail car or
locomotive or indirectly on a
bogie, also called a
truck. Wheels are
cast or
forged (wrought) and are heat-treated to have a specific hardness. New wheels are trued, using a
lathe, to a specific profile before being pressed onto an axle. All wheel profiles need to be periodically monitored to ensure proper
wheel-rail interface. Improperly trued wheels increase
rolling resistance, reduce
energy efficiency and may create unsafe operation. A railroad wheel typically consists of two main parts: the wheel itself, and the
tire (or
tyre) around the outside. A rail tire is usually made from
steel, and is typically heated and pressed onto the wheel, where it remains firmly as it shrinks and cools. Monobloc wheels do not have encircling tires, while
resilient rail wheels have a resilient material, such as
rubber, between the wheel and tire.