Wheelset (rail transport)
A wheelset is the wheel-axle assembly of a railroad car. The frame assembly beneath each end of a car, railcar or locomotive that holds the wheelsets is called the bogie (or truck in North America). Most North American freight cars have two bogies with two or three wheelsets, depending on the type of car; short freight cars generally have no bogies but instead have two wheelsets.
Two-axle cars operating on lines with sharp curves, such as Queensland Railways, used Grovers bogies.
Rubber-tyred metros feature special wheelsets with rubber tires outside of the special flanged steel wheels. The unusually large flanges on the steel wheels guide the bogie through standard railroad switches and in addition keep the train from derailing in case the tires deflate.
Most wheels have a conical taper of about 1 in 20. The conical shape has the effect of helping steer the wheelset around curves, so that the wheel flanges rarely come into contact with sides of the rails. The rails generally slant inwards at the same rate as the wheel conicity. As the wheels approach a curve, they will tend to continue in a straight path, due to inertia of the railcar. This causes the wheelset to shift sideways as the track curves under it, so that the effective diameter of the outer wheels is greater than that of the inner ones. Since the wheels are joined rigidly by the axle, the outer wheels will travel farther, causing the train to naturally follow the curve. For more information on this process, see Hunting oscillation.
For its first hundred years, Queensland Railways used cylindrical wheels and vertical rails. Some modern systems, such as Bay Area Rapid Transit (BART) in San Francisco, use cylindrical wheels and flat-topped rails.
- Matthias N. Forney (1879; reprint 1974). The Railroad Car Builder's Dictionary. Dover Publications, Inc.
- White, John H. (1978). The American Railroad Passenger Car. Baltimore, MD: Johns Hopkins University Press. ISBN 0801819652. OCLC 2798188.
- John H. White, Jr. (1993). The American Railroad Freight Car. Johns Hopkins University Press.