2-4-0

2-4-0 (Porter)
Diagram of one small leading wheel, and two large driving wheels joined together with a coupling rod
Front of locomotive at left
LSWR 0298 Class or Beattie Well Tank
Equivalent classifications
UIC class1B, 1'B
French class120
Turkish class23
Swiss class2/3
Russian class1-2-0
First known tender engine version
First usec. 1830s-1840s
CountryUnited Kingdom
Evolved from2-2-0 & 2-2-2
BenefitsBetter adhesion with coupled wheels

Under the Whyte notation for the classification of steam locomotives, 2-4-0 represents the wheel arrangement of two leading wheels on one axle, four powered and coupled driving wheels on two axles and no trailing wheels. In most of North America it became known as a Porter.

The notation 2-4-0T indicates a tank locomotive of this wheel arrangement, on which its water and fuel is carried on board the engine itself, rather than in an attached tender. A subset is 2-4-0WT, a configuration in which the water is under the bolier in a well tank.