Wheelset (rail transport)#Special wheelsets

{{Short description|Pair of railroad wheels fixed on to an axle}}

{{redirect|Wheel tread|distance between centers of wheels|Wheel track}}

A wheelset is a pair of railroad vehicle wheels mounted rigidly on an axle. Wheelsets are often mounted in a bogie ("truck" in North America) – a pivoted frame assembly holding at least two wheelsets – at each end of the vehicle. Most modern freight cars and passenger cars have bogies each with two wheelsets, but three wheelsets (or more) are used in bogies of freight cars that carry heavy loads, and three-wheelset bogies are under some passenger cars. Four-wheeled goods wagons that were once near-universal in Europe and Great Britain and their colonies have only two wheelsets; in recent decades such vehicles have become less common as trainloads have become heavier.

Conical wheel-tread

Most train wheels have a conical taper of about 1 in 20 to enable the wheelset to follow curves with less chance of the wheel flanges coming in contact with the rail sides, and to reduce curve resistance. The rails generally slant inwards at 1 in 40, a lesser angle than the wheel cone. Without the conical shape, a wheel would tend to continue in a straight path due to the inertia of the rail vehicle, causing the wheelset to move towards the outer rail on the curve. The cone increases the effective diameter of the wheel as it moves towards the outer rail, and since the wheels are mounted rigidly on the axle, the outer wheels travel slightly farther, causing the wheelsets to more efficiently follow the curve. Abnormal wear at the wheel–rail interface is thus avoided,{{cite journal|last=Tuzik|first=Bob|title=Taking the Long View: 20 years of Wheel/Rail Interaction (Part 1 of 2) |url=http://interfacejournal.com/archives/882 |journal=Interface: The Journal of Wheel/Rail Interaction|date=8 January 2014}} along with the loud, piercing, very high-pitched squeal which usually results from it – especially evident on curves in tunnels, stations and elevated track, due to flat surfaces slipping and flanges grinding along the rail. However, if the degree of conicality is inappropriate for the suspension and track, an unpleasant oscillation can occur at high speeds. Recent research is also showing that marginal changes to wheel and rail profiles can improve performance further.{{cite journal|last=Tuzik|first=Bob|title=Taking the Long View: 20 years of Wheel/Rail Interaction (Part 2 of 2) |url=http://interfacejournal.com/archives/1008 |journal=Interface: The Journal of Wheel/Rail Interaction|date=22 April 2014}}

Not all railroads have employed conical-tread wheels. The Bay Area Rapid Transit (BART) system in San Francisco, built with cylindrical wheels and flat-topped rails, started to re-profile the wheels in 2016 with conical treads after years of complaints about the squeal by its passengers.{{cite magazine|title=The Four-Year Fight to Make San Francisco's Subway Stop Screaming|date=2016-09-02|magazine=Wired|url=https://www.wired.com/2016/09/three-year-fight-make-san-franciscos-subway-stop-screaming/}} Australia's Queensland Railways used cylindrical wheels and vertical rails until the mid-1980s, when considerably higher train loads made the practice untenable.{{cite magazine|title=Radial wheeled rolling stock on the Queensland Railways |last=Knowles |first=J.W. |date=April 1974 |magazine= Bulletin |location=Burwood NSW |publisher=Australian Railway Historical Society |issn= 0005-0105 |volume=XXV |issue=438 |pages= 75–92}}{{cite magazine|title=The Queensland Railways and its cylindrical wheels |last=Knowles |first=John |date=December 1981 |magazine=Sunshine Express |location=Brisbane |publisher=Australian Railway Historical Society Queensland Division |volume=17 |issue=189 |page= 241}}{{cite magazine|title=More on the Queensland Railways and its cylindrical wheels |last=Knowles |first=John |date=September 1983 |magazine=Sunshine Express |location=Brisbane |publisher=Australian Railway Historical Society Queensland Division |volume=19 |issue=210 |page= 210}}

Specialised wheelsets

{{multiple image |width=260 |align=center

|image1=Bogie-metro-Meteor-p1010692.jpg

|image2=Système de guidage Translohr - Annoté.svg

|caption1=Bogie of a rubber-tyred electric multiple unit of the Paris Métro

|caption2=Translohr twin wheelet. 1: Pavement. 2: Gap (empty space). 3: Guide rail. 4: Resin. 5: Flange. 6: Spring. 7: Tyre.

}}

Some rubber-tyred metros feature special wheelsets with rubber tyres outside of deep-flanged steel wheels, which guide the bogie through standard railroad switches and keep the train from derailing if a tyre deflates. The system was originally conceived by Michelin for the Paris Métro; the first line opened in 1956.

Gallery

File:Denney Axle.jpg|Denney axle

File:Rollingstock axle.jpg|Railroad car wheels are rigidly mounted on an axle to rotate in unison.

File:SBB Cargo Güterwagen Radsätze.jpg|Swiss Federal Railways wheelsets with fitted journals

File:Rail axl at Texas Transportation museum.JPG|Wheelset from a railroad speeder. The wheels are pressed steel and the flanges are smaller than those of full-sized rail vehicles.

File:GWR Spoked wagon wheels.jpg|A wheelset from a Great Western Railway wagon, showing a plain bearing end

File:Bettendorf truck at Illinois Railway Museum.JPG|A freight bogie of the Bettendorf pattern, which became standard in North America and elsewhere

File:Пам.Энгельса29 КП Метро Штангист в каске.JPG|Wheelset as part of a welded sculpture in Kharkiv

File:Heidelberg funicular wheelset.jpg|Wheelset of a two-rail funicular with the Abt switch turnout

File:Muzeum MHD, dvoukolí vozu petřínské lanovky 1891.jpg|Funicular wheelset with Abt rack and pinion brake

File:Budapešť,_Városmajor,_pomník_zubačky.jpg|Wheelset of a rack railway

References

External links

{{Cite web|title=APTA PR-CS-RP-003-98 Recommended Practice for Developing a Clearance Diagram for Passenger Equipment 5.3.2.1 Design tolerances|url=http://www.apta.com/resources/standards/Documents/APTA-PR-CS-RP-003-98.pdf|website=APTA.com|publisher=American Public Transportation Association|date=1998-03-26|access-date=2015-01-17}}

Category:Bogie