The 439 Class, nicknamed the Bicycle class because of its unusual appearance, was a series of six 2-4-0 mixed-traffic engines designed by Joseph Armstrong for the Great Western Railway, and built at Swindon Works in 1868. The "Bicycles" worked at Northern Division sheds, running between Wolverhampton and Chester.
Numbered in the series 439-444, the running plate of these inside-framed locomotives was raised, without splashers, above each of the large (6 ft 1 in or 1.854 m) driving wheels, rather giving the impression of bicycle wheels and mudguards.
Most of the class was renewed at Wolverhampton Works under George Armstrong in 1885/6; the renewals were more conventional in appearance, with large splashers, but the class's nickname stuck. At first the renewals also ran on the same routes as their predecessors, though later some were transferred further south.