On a steam locomotive, a driving wheel is a powered wheel which is driven by the locomotive's pistons. On a conventional, non-articulated locomotive, the driving wheels are all coupled together with side rods ; normally one pair is directly driven by the main rod which is connected to the end of the piston rod; power is transmitted to the others through the side rods.
The driving wheels (boxed) on Pennsylvania Railroad 1737
Traction motor for a German locomotive
Half of the driving wheels of Milwaukee Road 261
One of six 6 ft 8 in (2.03 m) driving wheels belonging to 60163 Tornado
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 to heat water in the locomotive's boiler to the point where it becomes gaseous and its volume increases 1,700 times. Functionally, it is a steam engine on wheels.
LNER Class A4 4468 Mallard is officially the fastest steam locomotive, reaching 126 mph (203 km/h) on 3 July 1938.
LNER Class A3 4472 Flying Scotsman was the first steam locomotive to officially reach 100 mph (160 km/h), on 30 November 1934.
The Salamanca locomotive
The Locomotion at Darlington Railway Centre and Museum