Train wheel

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 (UK), also called a truck (North America). 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.

Most train wheels have a conical geometry, which is the primary means of keeping the train's motion aligned with the track. Train wheels have a flange on one side to keep the wheels, and hence the train, running on the rails, when the limits of the geometry based alignment are reached, e.g. due to some emergency or defect. See Hunting oscillation. Some wheels have a cylindrical geometry, where flanges are essential to keep the train on the rail track.

Crank pin: A pin protruding from a wheel into a main or coupling rod.

Wheels used for Road-rail vehicles are normally smaller than those found on other types of rollingstock (such as locomotives or carriages). This is because the wheel has to be stored clear of the ground when the vehicle is in road-going mode - Such wheels can be as small as 245 mm (9.65 in) in diameter. In Australia, wheels for Road-rail vehicles should comply with the requirements of AS7514.4 which is the standard for infrastructure maintenance vehicle wheels.

...
Wikipedia