6-8-6

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]

Notes

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v t e Steam locomotive wheel arrangements
Single engine types	0-2-2 0-2-4 2-2-0 2-2-2 2-2-4 4-2-0 4-2-2 4-2-4 6-2-0 0-3-0 0-4-0 0-4-2 0-4-4 0-4-6 2-4-0 2-4-2 2-4-4 2-4-6 4-4-0 4-4-2 4-4-4 4-4-6 0-6-0 0-6-2 0-6-4 2-6-0 2-6-2 2-6-4 2-6-6 4-6-0 4-6-2 4-6-4 0-8-0 0-8-2 0-8-4 2-8-0 2-8-2 2-8-4 2-8-6 4-8-0 4-8-2 4-8-4 4-8-6 6-8-6 0-10-0 0-10-2 2-10-0 2-10-2 2-10-4 4-10-0 4-10-2 0-12-0 2-12-0 2-12-2 2-12-4 4-12-2 4-14-4
Divided drive and Duplex engine types	0-2-2-0 2-2-2-0 2-2-2-2 2-2-4-0 4-2-2-0 2-4-6-2 4-4-4-4 6-4-4-6 4-4-6-4 4-6-4-4
Articulated locomotives Garratt and Meyer types	0-4-0+0-4-0 2-4-0+0-4-2 2-4-2+2-4-2 4-4-2+2-4-4 0-6-0+0-6-0 0-6-2+2-6-0 2-6-0+0-6-2 2-6-2+2-6-2 4-6-0+0-6-4 4-6-2+2-6-4 4-6-4+4-6-4 2-8-0+0-8-2 2-8-2+2-8-2 4-8-0+0-8-4 4-8-2+2-8-4 4-8-4+4-8-4
Articulated locomotives Fairlie and Mallet types (includes Triplex types)	0-4-4-0 0-4-4-2 2-4-4-0 2-4-4-2 0-6-6-0 2-6-6-0 2-6-6-2 2-6-6-4 2-6-6-6 2-6-8-0 4-6-6-2 4-6-6-4 0-8-6-0 0-8-8-0 2-8-8-0 2-8-8-2 2-8-8-4 4-8-8-2 4-8-8-4 2-10-10-2 2-8-8-8-2 2-8-8-8-4
Articulated locomotives Engerth types	0-4-4 0-4-6 2-6-2 0-6-4 0-6-4-0 0-8-4 0-8-6
Geared locomotives	Shay Climax Heisler Willamette
Other notation forms: AAR Swiss UIC