# Train wheel

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Wheel designed for railway tracks

Not to be confused with [Training wheels](/source/Training_wheels).

Both wheels of a [wheelset](/source/Wheelset_(rail_transport)) rotate at the same rate because the wheels are fixed rigidly on the axle

A **train wheel** or **rail wheel** is a type of [wheel](/source/Wheel) specially designed for use on [railway tracks](/source/Track_(rail_transport)). The wheel acts as a rolling component, typically [press fitted](/source/Press_fit) on to an [axle](/source/Axle) and mounted directly on a [railway carriage](/source/Railroad_car) or [locomotive](/source/Locomotive), or indirectly on a [bogie](/source/Bogie) (CwthE) or truck (NAmE). The powered wheels under the locomotive are called [driving wheels](/source/Driving_wheel). Wheels are initially [cast](/source/Casting) or [forged](/source/Forging) and then heat-treated to have a specific hardness.[1] New wheels are machined using a [lathe](/source/Lathe) to a standardised shape, called a profile. All wheel profiles are regularly checked to ensure proper [interaction between the wheel and the rail](/source/Wheel-rail_interface).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] Incorrectly profiled wheels and worn wheels can increase [rolling resistance](/source/Rolling_resistance), reduce [energy efficiency](/source/Energy_efficiency_in_transport) and may even cause a [derailment](/source/Derailment).[2] The [International Union of Railways](/source/International_Union_of_Railways) has defined a standard wheel diameter of 920 mm (36 in), although smaller sizes are used in some [rapid transit](/source/Rapid_transit) railway systems and on [ro-ro carriages](/source/Rolling_highway).[3]

## Wheel geometry and flange

See also: [Derailment](/source/Derailment), [Adhesion railway](/source/Adhesion_railway), and [Hunting oscillation](/source/Hunting_oscillation)

A railway wheel's [tread](/source/Wheelset_(rail_transport)#Conical_wheel-tread) and [flange](#Wheel_geometry_and_flange) and its relationship to the load-bearing rail

The running surface ("tread" or "rim") of most train wheels is [conical](/source/Cone), which serves as the primary means of keeping the train aligned centrally on the [track](/source/Track_(rail_transport)) while in motion. On curves, the [wheelset](/source/Wheelset_(rail_transport)) becomes "self-steering" because of this coning: when one wheel is pushed closer to the adjacent (outer) rail, it presents a bigger circumference to the rail than when centred on the track. Simultaneously, the inner wheel presents a smaller circumference to its rail. The difference between the distances travelled by each wheel for each rotation of the axle causes the wheelset to follow the curve of the track.[4] If a strong sideways force is experienced – for example, when the radius of a curve is smaller than normal or there are defects in the track alignment – the wheelset will depart from its equilibrium. That is when a projection on the inner side of each wheel, called a flange, constrains the wheelset from moving further and derailing.[5]

## Wheel arrangement

Main article: [Wheel arrangement](/source/Wheel_arrangement)

The number of wheels per locomotive or car varies in both size and number to accommodate the needs of the vehicle. Regardless of these factors, pairs of identically sized wheels are always affixed to a straight axle as a singular unit, called a [wheelset](/source/Wheelset_(rail_transport)).[4]

## Wheels for road–rail vehicles

The small rail wheels fitted to road–rail vehicles allow them to be stowed away when the vehicle is in road-going mode.

Wheels used for [road–rail vehicles](/source/Road%E2%80%93rail_vehicle) are normally smaller than those found on other types of [rolling stock](/source/Rolling_stock), such as locomotives or carriages, because the wheel has to be stowed 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.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## Railway wheel and tire

Main article: [Railway tire](/source/Railway_tire)

Modern railway wheels are usually machined from a single casting, also known as monobloc wheels.[6] Some wheels, however, are made of two parts: the wheel core, and a tyre (CwthE) or [tire](/source/Tire) (NAmE) around the perimeter. Separate tyres have been a component of some rolling stock, their purpose being to provide a replaceable wearing element – an important factor in the steam locomotive era with their costly [spoked](/source/Spoke) construction. In modern times the tyre is invariably made from [steel](/source/Steel), which is stronger than the [cast iron](/source/Cast_iron) of earlier eras. It is typically heated and pressed on to the wheel before it cools and shrinks. *Resilient rail wheels* have a resilient material, such as [rubber](/source/Rubber), between the wheel and tyre. Failure of this type of wheel was one of the causes leading to the [Eschede high-speed train crash](/source/Eschede_train_disaster#Wheel_design).[6]

## Causes of damage

The most common cause of wheel damage is severe braking, including sudden braking, braking on steep gradients and braking with heavy loads. The [brake shoes](/source/Railway_brake) (or brake blocks) are applied directly to the wheel surface, which generates immense amounts of [thermal energy](/source/Thermal_energy): under normal operation, a wheel may reach a tread temperature of 550 °C (1,022 °F).[7] Under severe braking conditions, the generated thermal energy can contribute to [thermal shock](/source/Thermal_shock) or alteration of the wheel's mechanical properties. Ultimately, acute thermal loading leads to a phenomenon called [spalling](/source/Spall). Alternatively, severe braking or [low adhesion](/source/Slippery_rail) may stop the rotation of the wheels while the vehicle is still moving, which may cause a [flat spot](/source/Flat_spot) on the [wheel-rail interface](/source/Wheel%E2%80%93rail_interface) and localised heat damage.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

Modern railway wheels are manufactured reasonably thickly to provide an allowance of wear material, since worn wheel profiles or wheels with a flat spot can be machined on a wheel lathe if there is sufficient thickness of material remaining.[8]

## Guide wheel

[Rubber-tyred metros](/source/Rubber-tyred_metro) with a central [guide rail](/source/Guide_rail#Railway_guide_rail), such as the [Busan Metro](/source/Busan_Metro_Line_4), [Lille Metro](/source/Lille_Metro) and the [Sapporo Municipal Subway](/source/Sapporo_Municipal_Subway) as well as [rubber-tyred trams](/source/Rubber-tyred_tram) have **guide wheels**.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

Left: diagram of the [Translohr](/source/Translohr) [guide rail](/source/Guide_rail#Railway_guide_rail) (green) and the tram's **guide wheels** (red). Right: cross section of the guide [rail](/source/Rail_profile) and **guide wheel** of the Bombardier's [GLT](/source/Bombardier_Guided_Light_Transit)

## See also

- [Adhesive weight](/source/Adhesive_weight)

- [Cycloid](/source/Cycloid) and [trochoid](/source/Trochoid)

- [Wheelset (rail transport)#Conical wheel-tread](/source/Wheelset_(rail_transport)#Conical_wheel-tread)

## References

1. **[^](#cite_ref-1)** Lewis, R.; Olofsson, U. (25 September 2009). [*Wheel–Rail Interface Handbook*](https://www.sciencedirect.com/book/9781845694128/wheel-rail-interface-handbook). Elsevier Science. [ISBN](/source/ISBN_(identifier)) [9781845694128](https://en.wikipedia.org/wiki/Special:BookSources/9781845694128). Retrieved 29 October 2020.

1. **[^](#cite_ref-2)** Lewis, Roger; Olofsson, Ulf (2009). *Wheel-rail interface handbook*. Boca Raton, Florida: CRC Press. [ISBN](/source/ISBN_(identifier)) [978-1-61583-153-1](https://en.wikipedia.org/wiki/Special:BookSources/978-1-61583-153-1). [OCLC](/source/OCLC_(identifier)) [500906475](https://search.worldcat.org/oclc/500906475).

1. **[^](#cite_ref-3)** Licitra, Gaetano (6 September 2012). [*Noise Mapping in the EU: Models and Procedures*](https://books.google.com/books?id=a9bKBQAAQBAJ&dq=train+wheels+rim+monoblock&pg=PA83). CRC Press. [ISBN](/source/ISBN_(identifier)) [978-0-203-84812-8](https://en.wikipedia.org/wiki/Special:BookSources/978-0-203-84812-8).

1. ^ [***a***](#cite_ref-:0_4-0) [***b***](#cite_ref-:0_4-1) ["Book: The Contact Patch"](https://the-contact-patch.com/book/rail/r1610-the-wheelset). *the-contact-patch.com*. Retrieved 29 October 2020.

1. **[^](#cite_ref-5)** Richard Feynman (1983). [*Feynman: how the train stays on the track*](https://www.youtube.com/watch?v=y7h4OtFDnYE). *Fun to Imagine*. BBC TV – via YouTube.com.

1. ^ [***a***](#cite_ref-:1_6-0) [***b***](#cite_ref-:1_6-1) Milne, Ian; Ritchie, R. O.; Karihaloo, B. L. (25 July 2003). [*Comprehensive Structural Integrity*](https://books.google.com/books?id=hpc60yCsTPcC&dq=monoblock+train+wheels+advantage&pg=PA56). Elsevier. [ISBN](/source/ISBN_(identifier)) [978-0-08-049073-1](https://en.wikipedia.org/wiki/Special:BookSources/978-0-08-049073-1).

1. **[^](#cite_ref-7)** Peters, Carsten J.; Eifler, Dietmar (1 November 2009). ["Influence of Service Temperatures on the Fatigue Behaviour of Railway Wheel and Tyre Steels*"](https://www.degruyter.com/document/doi/10.3139/120.110094/html). *Materials Testing*. **51** (11–12): 748–754. [Bibcode](/source/Bibcode_(identifier)):[2009MTest..51..748P](https://ui.adsabs.harvard.edu/abs/2009MTest..51..748P). [doi](/source/Doi_(identifier)):[10.3139/120.110094](https://doi.org/10.3139%2F120.110094). [ISSN](/source/ISSN_(identifier)) [2195-8572](https://search.worldcat.org/issn/2195-8572). [S2CID](/source/S2CID_(identifier)) [135684020](https://api.semanticscholar.org/CorpusID:135684020).

1. **[^](#cite_ref-8)** Nielsen, J. (1 January 2009). ["Out-of-round railway wheels"](http://www.sciencedirect.com/science/article/pii/B9781845694128500082). In Lewis, R.; Olofsson, U. (eds.). *Wheel–Rail Interface Handbook*. Woodhead Publishing. pp. 245–279. [doi](/source/Doi_(identifier)):[10.1533/9781845696788.1.245](https://doi.org/10.1533%2F9781845696788.1.245). [ISBN](/source/ISBN_(identifier)) [978-1-84569-412-8](https://en.wikipedia.org/wiki/Special:BookSources/978-1-84569-412-8). Retrieved 29 October 2020.

## External links

- ["APTA PR-CS-RP-003-98 Recommended Practice for Developing a Clearance Diagram for Passenger Equipment 5.3.2.1 Design tolerances"](http://www.apta.com/resources/standards/Documents/APTA-PR-CS-RP-003-98.pdf) (PDF). *APTA.com*. [American Public Transportation Association](/source/American_Public_Transportation_Association). 26 March 1998. Retrieved 17 January 2015.

v t e Locomotive design Cab positioning Short hood / Long hood Cab forward Sharknose Steeplecab Cab unit Hood unit Cowl unit Boxcab Comfort cab Dual Control Stand Wheel arrangement AAR wheel arrangement UIC classification Swiss classification Whyte notation Valve gear types Allan Baker Bagnall–Price Baguley Bulleid Caprotti Gab Gooch Gresley Hackworth Joy Kuhn slide Lentz Southern Stephenson Walschaerts Bogie types AAR type A switcher truck Arnoux system Articulated bogie Bissel truck Blomberg B Cleminson system Grovers bogie Jacobs bogie Krauss-Helmholtz bogie Mason Bogie Pony truck Radial steering truck Scheffel bogie Schwartzkopff-Eckhardt II bogie Other running gear elements Adams axle Axlebox Beugniot lever Carrying wheel Coupled wheel Driving wheel Equalising beam Gölsdorf axle Journal box Klien-Lindner axle Leading wheel Luttermöller axle Radial axle Railway tire Road–rail vehicle Trailing wheel Train wheel Wheelset Exhaust system types Giesl Kylchap Kylpor Lemaître Lempor Lemprex Common exhaust system elements Blastpipe Smokebox Chimney

Authority control databases International GND National United States Israel Other Yale LUX

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Adapted from the Wikipedia article [Train wheel](https://en.wikipedia.org/wiki/Train_wheel) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Train_wheel?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.