The leading wheel or leading axle or pilot wheel of a steam locomotive
is an unpowered wheel or axle located in front of the driving wheels.
The axle or axles of the leading wheels are normally located on a
leading truck. Leading wheels are used to help the locomotive
negotiate curves and to support the front portion of the boiler.
Importantly, the leading bogie does not have simple rotational motion
about a vertical pivot, as might first be thought. It must also be
free to slip sideways to a small extent (otherwise the locomotive is
unable to follow curves accurately – a point lost on the 19th
century railway pioneers), and some kind of springing
mechanism is normally included to control this movement and give a
tendency to return to centre. The sliding bogie of this type was
patented by William Adams in 1865. The first use of leading wheels
is commonly attributed to
John B. Jervis
AAR wheel arrangement Adams axle Trailing wheel UIC classification Whyte notation
^ Simmons, Jack; Biddle, Gordon (1997). The Oxford Companion to British Railway History. Oxford: Oxford University Press. ISBN 0-19-211697-5. ^ Rolt, Lionel (1955). Red for Danger. London: Bodley Head. ISBN 0-7153-7292-0. ^ Gladstone at the National Railway Museum, York Archived 2006-10-15 at the Wayback Machine. accessed 22 December 2006.
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Locomotive running and valve gear
Allan Baker Bagnall-Price Baguley Bulleid Caprotti Gab Gooch Gresley Hackworth Joy Kuhn slide Lentz Southern Stephenson Walschaerts
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 Tr