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

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

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