Wheelset (rail transport)

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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.

Grovers bogie[edit]

Two-axle cars operating on lines with sharp curves, such as Queensland Railways, used Grovers bogies.[1][2][3]

Special wheelsets[edit]

Bogie from an MP 89 Paris Métro rolling stock showing the two special wheelsets

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.

Conical shape[edit]

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.{1,2,3)<1>J W Knowles, Radial Wheeled Rolling Stock on the Queensland Railways, Australian Railway Historical Society Bulletin, Vol XXV, No 438, April 1974, pp 75 - 92; <2> John Knowles, The Queensland Railways and its Cylindrical Wheels,Sunshine Express, Vol 17, No. 189., December 1981, p 241. <3> John Knowles, More on the Queensland Railways and its Cylindrical Wheels,Sunshine Express, Vol 19, No. 210, September 1983, p 210.> With uninclined rails and cylindrical wheels, the wheel squeal from trains taking curves on that railway was slight. When that railway adopted coned wheels and inclined rails from the mid 1980s, the wheel squeal from trains curving in the same locations and at the same speeds increased immenseley. Some modern systems, such as Bay Area Rapid Transit (BART) in San Francisco, use cylindrical wheels and flat-topped rails.


A wheelset from a GWR wagon, showing a plain bearing end 
Two wheelsets with journal boxes in a North American (Bettendorf-style) freight bogie displayed at the Illinois Railway Museum
Wheelset Monument in Kharkov 
Rail axle at the Texas Transportation Museum 
Railway wheel flange, left & tram wheel flange, right 
Railroad car wheels are affixed to a straight axle, such that both wheels rotate in unison. This is called a wheelset. 
Track = wheel gauge (measured between the gauge or flange reference lines of the flanges of railroad wheels

See also[edit]


  • Matthias N. Forney (1879; reprint 1974). The Railroad Car Builder's Dictionary. Dover Publications, Inc.  Check date values in: |date= (help)
  • 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.