British steam locomotives are described by their wheel arrangement — a quick shorthand for the number of wheels and how they are grouped. The system used here is the Whyte notation, and once you know it you can read any locomotive at a glance.
How the notation works
The Whyte notation counts the wheels in groups, front to back:
[leading wheels] – [driving wheels] – [trailing wheels]
- Leading wheels — small guiding wheels at the front that steer the engine into curves.
- Driving wheels — the large powered wheels in the middle, coupled together.
- Trailing wheels — small wheels at the back, often there to support a large firebox.
So a 4-6-2 has four leading wheels, six driving wheels and two trailing wheels. A T on the end (e.g. 0-6-0T) marks a tank engine, which carries its own water and coal rather than a separate tender.
carrying / guiding wheel driving wheel(side view — one wheel shown per axle)
The common British wheel arrangements
Two coupled axles, no carrying wheels — short, nimble shunting and industrial engines.
The classic British goods engine: all weight on the coupled wheels for maximum grip. Thousands were built. The tank version (0-6-0T) includes the famous GWR 5700 pannier tanks and the little LBSCR “Terrier”.
A heavier all-adhesion goods type, favoured by the LNWR and others for mineral traffic.
A single leading axle ahead of two coupled axles — the typical fast passenger engine of the mid-Victorian years.
A leading bogie for steady running at speed: the classic British express locomotive for decades, e.g. the GWR City class and the LSWR T9 “Greyhound”.
A single pair of large driving wheels for fast, free running — elegant but limited in grip, as on the celebrated Stirling Single.
A trailing axle behind the drivers allows a larger firebox, e.g. the GNR Atlantic.
A versatile mixed-traffic type — a leading pony truck and three coupled axles, e.g. the LMS “Crab” and the GWR 4300.
Six coupled wheels with a leading bogie — the workhorse express and mixed-traffic layout, as on the Stanier Black Five and the GWR Castles and Kings.
The big-boilered express type: leading bogie, six coupled drivers and a trailing truck under a large firebox. Britain’s most famous engines, including the record-breaking LNER A4 and the LMS Princess Coronation.
Usually a tank engine (2-6-4T) for fast suburban and branch work, e.g. the Fairburn 2-6-4T.
A tank type (0-4-4T) with a trailing bogie for steady bunker-first running on suburban trains, e.g. the LSWR M7.
A leading pony truck and four coupled axles — the standard British heavy-freight type, e.g. the Stanier 8F and GWR 2800.
Five coupled axles for the heaviest freight, as on the mighty BR 9F — the last steam type built by British Railways.
The class names
Several arrangements picked up nicknames, often American in origin: Atlantic (4-4-2), Pacific (4-6-2), Mogul (2-6-0), Prairie (2-6-2), Mikado (2-8-2) and Consolidation (2-8-0). The names stuck and are still used by enthusiasts today.
More in this section: The Parts of a Steam Locomotive · How a Steam Locomotive Works · browse the locomotive classes.