Under the Whyte notation for the classification of steam locomotives by wheel arrangement, 6-8-6 represents the arrangement of six unpowered leading wheels arranged into a three-axle leading truck, eight powered driving wheels, and six unpowered trailing wheels arranged into a three-axle trailing truck.

Front of locomotive to the left
The single S2, No. 6200, in a PRR promotional image.

Other equivalent classifications are:

The only known example of the 6-8-6 wheel arrangement is the experimental Pennsylvania Railroad S2 steam turbine locomotive.[1]


  1. ^ Staufer & Pennypacker 1962, pp. 240–242


  • Staufer, Alvin F.; Pennypacker, Bert (1962). Pennsy Power: Steam and Electric Locomotives of the Pennsylvania Railroad, 1900-1957. Research by Martin Flattley. Carollton, Ohio: Alvin F. Staufer. ISBN 978-0-9445-1304-0.