On a

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the loco ...

, a driving wheel is a powered wheel which is driven by the

locomotive A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the ...

's pistons (or

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating ...

, in the case of a steam turbine locomotive). On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods (also known as coupling rods); normally one pair is directly driven by the

main rod A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the cranksh ...

(or

connecting rod A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the crank ...

) which is connected to the end of the piston rod; power is transmitted to the others through the side rods. On

diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engi ...

and

electric locomotive An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or a supercapacitor. Locomotives with on-board fuelled prime movers, such as diesel engines or g ...

s, the driving wheels may be directly driven by the

traction motor A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives, electric or hydrogen vehicles, elevators or electric multiple unit. Traction motors are used in electrically powered rail vehicles ( electric multip ...

s. Coupling rods are not usually used, and it is quite common for each axle to have its own motor. Jackshaft drive and coupling rods were used in the past (e.g. in the Swiss Crocodile locomotive) but their use is now confined to

shunting locomotives A switcher, shunter, yard pilot, switch engine, yard goat, or shifter is a small railroad locomotive used for manoeuvring railroad cars inside a rail yard in a process known as ''switching'' (US) or ''shunting'' (UK). Switchers are not inte ...

. On an articulated locomotive or a duplex locomotive, driving wheels are grouped into sets which are linked together within the set.

Diameter

Driving wheels are generally larger than leading or trailing wheels. Since a conventional steam locomotive is directly driven, one of the few ways to '

gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic ...

' a locomotive for a particular performance goal is to size the driving wheels appropriately. Freight locomotives generally had driving wheels between in diameter; dual-purpose locomotives generally between , and passenger locomotives between or so. The driving wheels on express passenger locomotives have come down in diameter over the years, e.g. from on the GNR Stirling 4-2-2 of 1870 to on the SR Merchant Navy Class of 1941. This is because improvements in valve design allowed for higher piston speeds.

Flangeless wheels

Some long wheelbase locomotives (four or more coupled axles) were equipped with blind drivers. These were driving wheels without the usual

flange A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...

s, which allowed them to negotiate tighter curves without binding. Some three-driving-axle locomotives also had flangeless wheels on the middle axle, such as the

NZR WH class The NZR WH class was a class of three steam locomotives built by Manning Wardle in 1884 for service on New Zealand's private Wellington and Manawatu Railway Company (WMR). They did not acquire their WH classification until 1908 when WMR was nat ...

Balancing

On locomotives with side rods, including most

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporizatio ...

and jackshaft locomotives, the driving wheels have weights to balance the weight of the coupling and connecting rods. The crescent-shaped balance weight is clearly visible in the picture on the right.

Whyte notation

In the Whyte notation, driving wheels are designated by the middle number or numbers in the set. The

UIC classification The UIC classification of locomotive axle arrangements, sometimes known as the German classification''The Railway Data File''. Leicester: Silverdale, 2000. p. 52. . or German system,Kalla-Bishop P.M. & Greggio, Luciano, ''Steam Locomotives'', Cre ...

system counts the number of axles rather than the number of wheels and driving wheels are designated by letters rather than numbers. The suffix 'o' is used to indicate independently-powered axles. The number of driving wheels on locomotives varied quite a bit. Some early locomotives had as few as two driving wheels (one axle). The largest number of total driving wheels was 24 (twelve axles) on the 2-8-8-8-2 and 2-8-8-8-4 locomotives. The largest number of coupled driving wheels was 14 (seven axles) on the ill-fated AA20 4-14-4 locomotive.

Other uses of the term ''driving wheel''

The term ''driving wheel'' is sometimes used to denote the ''

drive sprocket A sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain pass ...

'' which moves the

track Track or Tracks may refer to: Routes or imprints * Ancient trackway, any track or trail whose origin is lost in antiquity * Animal track, imprints left on surfaces that an animal walks across * Desire path, a line worn by people taking the shorte ...

on tracked vehicles such as

tank A tank is an armoured fighting vehicle intended as a primary offensive weapon in front-line ground combat. Tank designs are a balance of heavy firepower, strong armour, and good battlefield mobility provided by tracks and a powerful ...

s and

bulldozer A bulldozer or dozer (also called a crawler) is a large, motorized machine equipped with a metal blade to the front for pushing material: soil, sand, snow, rubble, or rock during construction work. It travels most commonly on continuous track ...

In popular culture

Many American roots artists, such as

The Byrds The Byrds () were an American rock band formed in Los Angeles, California, in 1964. The band underwent multiple lineup changes throughout its existence, with frontman Roger McGuinn (known as Jim McGuinn until mid-1967) remaining the sole con ...

, Tom Rush,

The Black Crowes The Black Crowes are an American rock band formed in Atlanta, Georgia, in 1984. Their discography includes eight studio albums, four live albums and several charting singles. The band was signed to Def American Recordings in 1989 by producer Ge ...

and the Canadian band

Cowboy Junkies Cowboy Junkies are an alternative country and folk rock band formed in Toronto, Ontario, Canada in 1985 by Alan Anton (bassist), Michael Timmins (songwriter, guitarist), Peter Timmins (drummer) and Margo Timmins (vocalist). The three Timminses ...

have performed a song written by David Wiffen called "Driving Wheel", with the lyrics "I feel like some old engine/ That's lost my driving wheel." These lyrics are a reference to the traditional blues song "Broke Down Engine Blues" by

Blind Willie McTell Blind Willie McTell (born William Samuel McTier; May 5, 1898 – August 19, 1959) was a Piedmont blues and ragtime singer and guitarist. He played with a fluid, syncopated fingerstyle guitar technique, common among many exponents of Piedmont bl ...

, 1931. It was later directly covered by

Bob Dylan Bob Dylan (legally Robert Dylan, born Robert Allen Zimmerman, May 24, 1941) is an American singer-songwriter. Often regarded as one of the greatest songwriters of all time, Dylan has been a major figure in popular culture during a career sp ...

and Johnny Winter. Many versions of the American folk song "

In the Pines "In the Pines", also known as "Where Did You Sleep Last Night?", "My Girl" and "Black Girl", is a traditional American folk song originating from two songs, "In the Pines" and "The Longest Train", both of whose authorship is unknown and date back ...

" performed by artists such as Leadbelly,

Mark Lanegan Mark William Lanegan (November 25, 1964 – February 22, 2022) was an American singer, songwriter, and poet. First becoming prominent as the lead singer for the early grunge band Screaming Trees, he was also known as a member of Queens of the ...

(on '' The Winding Sheet''), and

Nirvana ( , , ; sa, निर्वाण} ''nirvāṇa'' ; Pali: ''nibbāna''; Prakrit: ''ṇivvāṇa''; literally, "blown out", as in an oil lamp Richard Gombrich, ''Theravada Buddhism: A Social History from Ancient Benāres to Modern Colomb ...

(On '' MTV Unplugged In New York'') reference a decapitated man's head found in a driving wheel. In addition, it is likely that Chuck Berry references the locomotive driving wheel in "Johnny B. Goode" when he sings, "the engineers would see him sitting in the shade / Strumming with the rhythm that the drivers made."

References

* {{Locomotive running gear Steam locomotive technologies Train wheels