View source for Wheel arrangement

{{Short description|Classification system for rolling stocks}}
{{Refimprove|date=December 2009}}
[[File:Locotypes mod.gif|thumb|Locomotives of different types (Whyte and UIC wheel notation)]]

In [[rail transport]], a '''wheel arrangement''' or '''wheel configuration''' is a system of classifying the way in which wheels are distributed under a [[locomotive]].<ref>{{cite web |url=http://www.railway-technical.com/whlarr.shtml |title=Wheel Arrangements |publisher=Railway Technical Web Pages |date=1 August 2011 |access-date=1 August 2011 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304190511/http://www.railway-technical.com/whlarr.shtml |url-status=dead }}</ref> Several notations exist to describe the wheel assemblies of a locomotive by type, position, and connections, with the adopted notations varying by country.  Within a given country, different notations may also be employed for different kinds of locomotives, such as [[steam locomotive|steam]], [[electric locomotive|electric]], and [[diesel locomotive|diesel]] powered.

Especially in steam days, wheel arrangement was an important attribute of a locomotive because there were many different types of layout adopted, each wheel being optimised for a different use (often with only some being actually "driven"). Modern diesel and electric locomotives are much more uniform, usually with all axles driven.

==Major notation schemes==
{{Commons category|Wheel arrangements}}
{{worldwide|date=July 2024}}
The main notations are the [[Whyte notation]] (based on counting the wheels), the [[AAR wheel arrangement]] notation (based on counting either the axles or the [[bogie]]s), and the [[UIC classification of locomotive axle arrangements]] (based on counting either the axles or the bogies).

The Whyte notation is generally used for [[steam locomotive]]s throughout the [[United States]], [[Canada]], the [[United Kingdom]] and [[Ireland]]. For diesels and electrics, [[North America]] uses the AAR wheel arrangement scheme while British practice uses a slightly simplified form of the European UIC classification scheme (except for small diesel shunters, where Whyte notation is used).

In mainland [[Europe]], the UIC classification scheme is generally used for all locomotive types including steam, with some exceptions. In [[France]], the UIC classification is used for diesels and electrics while a scheme similar to the Whyte notation, but counting axles instead of wheels, is used for steam locomotives. Notably, [[Switzerland]] had its own separate notation system until 1989, with the [[Swiss locomotive and railcar classification]] now only retained for its [[narrow-gauge railway]]s.

*[[AAR wheel arrangement]]  -  Used largely throughout the US and Canada for diesel and electric locomotives.
*[[UIC classification of locomotive axle arrangements|UIC classification]]  -  Used in mainland Europe for all locomotive types. Used in the UK for electric and large diesel locomotives.
*[[Whyte notation]]  -  Used in North America, the UK and Ireland for steam locomotives, and for shunter locomotives (US: [[switcher locomotive]]s) in the UK.

== Comparison of wheel arrangements and wheel picture ==
{{original research|American name column|date=August 2024}}
{| class="wikitable sortable"
|-class="background6"
!VDEV/VMEV/UIC-system
!Whyte-notation
!American name
!Picture scheme<br><small>Locomotive front is to the left</small>
|-
|A1
|[[0-2-2]]
|Northumbrian
|[[File:WheelArrangement_0-2-2.svg|30px]]
|-
|A2
|[[0-2-4]]
|
|
|-
|1A
|[[2-2-0]]
|Planet
|[[File:WheelArrangement_2-2-0.svg|35px]]
|-
|1A1
|[[2-2-2]]
|Single, Jenny Lind, Patentee
|[[File:WheelArrangement_2-2-2.svg|40px]]
|-
|1A2
|[[2-2-4T|2-2-4]]
|Aerolite
|[[File:WheelArrangement_2-2-4.svg|45px]]
|-
|2{{prime}}A
|[[4-2-0]]
|Jervis
|[[File:WheelArrangement_4-2-0.svg|35px]]
|-
|2{{prime}}A1
|[[4-2-2]]
|
|[[File:WheelArrangement_4-2-2.svg|40px]]
|-
|2A2
|[[4-2-4T|4-2-4]]
|Huntington
|[[File:WheelArrangement_4-2-4.svg|50px]]
|-
|3A
|[[6-2-0]]
|Crampton
|[[File:WheelArrangement_6-2-0.svg|40px]]
|-
|N/A
|[[0-3-0]]
|
|[[File:WheelArrangement_0-6-0.svg|35px]]
|-
|B
|[[0-4-0]]
|Four-Wheel-Switcher
|[[File:WheelArrangement_0-4-0.svg|30px]]
|-
|B1
|[[0-4-2]]
|Olomana
|[[File:WheelArrangement_0-4-2.svg|35px]]
|-
|B2{{prime}}
|[[0-4-4T|0-4-4]]
|Forney four-coupled
|[[File:WheelArrangement_0-4-4.svg|40px]]
|-
|B3{{prime}}
|[[0-4-6]]
|
|
|-
|1B
|[[2-4-0]]
|Porter
|[[File:WheelArrangement_2-4-0.svg|40px]]
|-
|1{{prime}}B1{{prime}}
|[[2-4-2]]
|Columbia
|[[File:WheelArrangement_2-4-2.svg|40px]]
|-
|1B2{{prime}}
|[[2-4-4T|2-4-4]]
|Forney, Mason Bogie
|[[File:WheelArrangement_2-4-4.svg|45px]]
|-
|1B3{{prime}}
|[[2-4-6]]
|
|
|-
|2{{prime}}B
|[[4-4-0]]
|American, Eight-Wheeler
|[[File:WheelArrangement_4-4-0.svg|45px]]
|-
|2{{prime}}B1{{prime}}
|[[4-4-2 (locomotive)|4-4-2]]
|Atlantic
|[[File:WheelArrangement_4-4-2.svg|50px]]
|-
|2{{prime}}B2{{prime}}
|[[4-4-4]]
|Jubilee (CA), Reading (US)
|[[File:WheelArrangement_4-4-4.svg|55px]]
|-
|2{{prime}}B3{{prime}}
|[[4-4-6]]
|
|
|-
|C
|[[0-6-0]]
|Six-Wheel-Switcher
|[[File:WheelArrangement_0-6-0.svg|40px]]
|-
|C1
|[[0-6-2]]
|Webb, Branchline
|[[File:WheelArrangement_0-6-2.svg|45px]]
|-
|C2{{prime}}
|[[0-6-4]]
|
|[[File:WheelArrangement_0-6-4.svg|50px]]
|-
|1{{prime}}C
|[[2-6-0]]
|Mogul
|[[File:WheelArrangement_2-6-0.svg|45px]]
|-
|[[1{{prime}}C1{{prime}}]]
|[[2-6-2]]
|Prairie
|[[File:WheelArrangement_2-6-2.svg|50px]]
|-
|1{{prime}}C2{{prime}}
|[[2-6-4]]
|Adriatic, Lionel
|[[File:WheelArrangement_2-6-4.svg|55px]]
|-
|1{{prime}}C3{{prime}}
|[[2-6-6]]
|
|[[File:WheelArrangement_2-6-6.svg|60px]]
|-
|2{{prime}}C
|[[4-6-0]]
|Ten-Wheeler
|[[File:WheelArrangement_4-6-0.svg|50px]]
|-
|2{{prime}}C1{{prime}}
|[[4-6-2]]
|Pacific
|[[File:WheelArrangement_4-6-2.svg|55px]]
|-
|2{{prime}}C2{{prime}}
|[[4-6-4]]
|Hudson (NYC), Baltic (MR), Shore Line (NH)
|[[File:WheelArrangement_4-6-4.svg|60px]]
|-
|D
|[[0-8-0]]
|Eight-Wheel-Switcher
|[[File:WheelArrangement_0-8-0.svg|45px]]
|-
|D1
|[[0-8-2]]
|Transfer
|[[File:WheelArrangement_0-8-2.svg|50px]]
|-
|D2{{prime}}
|[[0-8-4T|0-8-4]]
|
|[[File:WheelArrangement_0-8-4.svg|55px]]
|-
|D3{{prime}}
|[[0-8-6]]
|
|
|-
|1{{prime}}D
|[[2-8-0]]
|Consolidation
|[[File:WheelArrangement_2-8-0.svg|50px]]
|-
|1{{prime}}D1{{prime}}
|[[2-8-2]]
|Mikado, MacArthur (USATC)
|[[File:WheelArrangement_2-8-2.svg|55px]]
|-
|1{{prime}}D2{{prime}}
|[[2-8-4]]
|Berkshire, Kanawha (C&O), Lima (B&M)&(IC)
|[[File:WheelArrangement_2-8-4.svg|60px]]
|-
|1{{prime}}D3{{prime}}
|[[2-8-6]]
|
|[[File:WheelArrangement_2-8-6.svg|65px]]
|-
|2{{prime}}D
|[[4-8-0]]
|Twelve-Wheeler, Mastodon
|[[File:WheelArrangement_4-8-0.svg|55px]]
|-
|2{{prime}}D1{{prime}}
|[[4-8-2]]
|Mountain, Mohawk (NYC), New Haven (NH)
|[[File:WheelArrangement_4-8-2.svg|60px]]
|-
|2{{prime}}D2{{prime}}
|[[4-8-4]]
|Northern, General Service (SP), Golden State (SP), Niagara (NYC), Wyoming (LV), Potomac (WM), Confederation (CN), Dixie (NC&St.L), Greenbrier (C&O), Laurentian (D&H), Montana (GN), Pocono (Lackawanna), 
|[[File:WheelArrangement_4-8-4.svg|65px]]
|-
|2D3
|[[4-8-6]]
|
|[[File:WheelArrangement_4-8-6.svg|70px]]
|-
|3{{prime}}D3{{prime}}
|[[6-8-6]]
|''Turbine'' (Pennsylvania Railroad Steam Turbine)
|[[File:WheelArrangement_6-8-6.svg|75px]]
|-
|E
|[[0-10-0]]
|Ten-Wheel Switcher
|[[File:WheelArrangement_0-10-0.svg|60px]]
|-
|E1{{prime}}
|[[0-10-2]]
|Union
|[[File:WheelArrangement_0-10-2.svg|65px]]
|-
|1{{prime}}E
|[[2-10-0]]
|Decapod
|[[File:WheelArrangement_2-10-0.svg|65px]]
|-
|2{{prime}}E
|[[4-10-0]]
|Mastodon, El Gobernador, 
|[[File:WheelArrangement_4-10-0.svg|70px]]
|-
|1{{prime}}E1{{prime}}
|[[2-10-2]]
|Santa Fe, Decapod (SP), Central (IC)
|[[File:WheelArrangement_2-10-2.svg|70px]]
|-
|1{{prime}}E2{{prime}}
|[[2-10-4]]
|Texas, Selkirk (CP), Colorado (CB&Q) 
|[[File:WheelArrangement_2-10-4.svg|75px]]
|-
|2{{prime}}E1{{prime}}
|[[4-10-2]]
|Southern Pacific, Overland (UP)
|[[File:WheelArrangement_4-10-2.svg|75px]]
|-
|F
|[[0-12-0]]
|Pennsylvania, Twelve-Wheel-Switcher
|[[File:WheelArrangement_0-12-0.svg|70px]]
|-
|1{{prime}}F
|[[2-12-0]]
|Centipede
|[[File:WheelArrangement_2-12-0.svg|75px]]
|-
|1{{prime}}F1{{prime}}
|[[2-12-2]]
|Javanic
|[[File:WheelArrangement_2-12-2.svg|80px]]
|-
|2{{prime}}F1{{prime}}
|[[4-12-2]]
|Union Pacific
|[[File:WheelArrangement_4-12-2.svg|85px]]
|-
|2{{prime}}G2{{prime}}
|[[4-14-4]]
|''Soviet'' (AA)
|[[File:WheelArrangement_4-14-4.svg|95px]]
|-
|A{{prime}}A
|[[0-2-2-0]]
|
|
|-
|B{{prime}}B
|[[0-4-4-0]]
|''nameless'' (Mallet)
|
|-
|B{{prime}}B1
|[[0-4-4-2]]
|''nameless'' (Mallet)
|
|-
|2{{prime}}BB2{{prime}}
|[[4-4-4-4]]
|''nameless'' (Pennsylvania Railroad Duplex)
|[[File:WheelArrangement_4-4-4-4.svg|80px]]
|-
|3{{prime}}BB3{{prime}}
|[[PRR S1|6-4-4-6]]
|
|[[File:WheelArrangement_6-4-4-6.svg|90px]]
|-
|2{{prime}}CB2{{prime}}
|[[4-6-4-4]]
|''nameless'' (Pennsylvania Railroad Duplex)
|[[File:WheelArrangement_4-6-4-4.svg|85px]]
|-
|C{{prime}}C
|[[0-6-6-0]]
|Old Maude (Mallet)
|[[File:WheelArrangement_0-6-6-0.svg|90px]]
|-
|(1{{prime}}C)C
|[[2-6-6-0]]
|nameless (Mallet)
|[[File:WheelArrangement_2-6-6-0.svg|90px]]
|-
|(1{{prime}}C)C1{{prime}}
|[[2-6-6-2]]
|nameless (Mallet)
|[[File:WheelArrangement_2-6-6-2.svg|90px]]
|-
|(1{{prime}}C)C2{{prime}}
|[[2-6-6-4]]
|''nameless'' (Simple articulated)
|[[File:WheelArrangement_2-6-6-4.svg|90px]]
|-
|(2{{prime}}C)C2{{prime}}
|[[4-6-6-4]]
|[[Union Pacific Challenger|Challenger]] (Simple articulated)
|[[File:WheelArrangement_4-6-6-4.svg|90px]]
|-
|(1{{prime}}C)C3{{prime}}
|[[2-6-6-6]]
|Allegheny, Blue Ridge (Simple articulated)
|[[File:WheelArrangement_2-6-6-6.svg|90px]]
|-
|D{{prime}}D
|[[0-8-8-0]]
|Angus (Mallet)
|[[File:WheelArrangement_0-8-8-0.svg|90px]]
|-
|(1{{prime}}D)D
|[[2-8-8-0]]
|Bull Moose (Mallet)
|[[File:WheelArrangement_2-8-8-0.svg|90px]]
|-
|(1{{prime}}D)D1{{prime}}
|[[2-8-8-2]]
|Chesapeake (C&O), Cab Forward (SP) (Mallet)
|[[File:WheelArrangement_2-8-8-2.svg|90px]]
|-
|(1{{prime}}D)D2{{prime}}
|[[2-8-8-4]]
|Yellowstone (Simple articulated)
|[[File:WheelArrangement_2-8-8-4.svg|90px]]
|-
|(2{{prime}}D)D1{{prime}}
|[[4-8-8-2]]
|Cab Forward (Simple articulated)
|[[File:WheelArrangement_4-8-8-2.svg|90px]]
|-
|(2{{prime}}D)D2{{prime}}
|[[4-8-8-4]]
|[[Union Pacific Big Boy|Big Boy]] (Simple articulated)
|[[File:WheelArrangement_4-8-8-4.svg|90px]]
|-
|(1{{prime}}E)E1{{prime}}
|[[2-10-10-2]]
|Virginian (Mallet)
|[[File:WheelArrangement_2-10-10-2.svg|90px]]
|-
|(1{{prime}}D1{{prime}})(1{{prime}}D1{{prime}})
|[[2-8-2+2-8-2]]
|Nameless, [[Garratt locomotive|Garratt]]
|[[File:WheelArrangement_2-8-2+2-8-2.svg|100px]]
|-
|(2{{prime}}C1{{prime}})(1{{prime}}C2{{prime}})
|[[4-6-2+2-6-4]]
|nameless (Garratt)
|[[File:WheelArrangement_4-6-2+2-6-4.svg|100px]]
|-
|(2{{prime}}C2{{prime}})(2{{prime}}C2{{prime}})
|[[4-6-4+4-6-4]]
|nameless (Garratt)
|[[File:WheelArrangement_4-6-4+4-6-4.svg|100px]]
|-
|(2{{prime}}D)(D2{{prime}})
|[[4-8-0+0-8-4]]
|nameless (Garratt)
|
|-
|(2{{prime}}D1{{prime}})(1{{prime}}D2{{prime}})
|[[4-8-2+2-8-4]]
|Double Mountain (Garratt)
|[[File:WheelArrangement_4-8-2+2-8-4.svg|100px]]
|-
|(2{{prime}}D2{{prime}})(2{{prime}}D2{{prime}})
|[[4-8-4+4-8-4]]
|nameless (Garratt)
|[[File:WheelArrangement_4-8-4+4-8-4.svg|100px]]
|}

== Geared steam locomotives ==
[[Geared steam locomotive]]s such as [[shay locomotive|Shays]], [[heisler locomotive|Heislers]], and [[climax locomotive|Climaxes]] do not have a standard wheel arrangement classification system. Instead of being classified by wheel arrangement, they are instead classified by their design and their number of [[bogie|trucks]].
:{| class="wikitable sortable"
|-class="background5"
!No. of trucks
!American name
!Picture scheme
|-
|2-truck
|Class A Shay, Class B Shay, Class A Climax, Class B Climax, Heisler
|oo oo	
|-
|3-truck
|Class C Shay, Class C Climax, Heisler
|oo oo oo	
|-
|4-truck
|Class D Shay
|oo oo oo oo	
|}
	
== See also ==
{{Wikidata property|P2978}}
* [[Bo-Bo]]
* [[Bo-Bo-Bo]]
* [[Co-Co locomotives]]

==References==
{{reflist}}
{{Locostyles}}
{{DEFAULTSORT:Wheel Arrangement}}
[[Category:Locomotives]]