Geared steam locomotive
This gearing is part of the machinery within the locomotive and should not be confused with the pinion that propels a rack locomotive along the rack between the rails. The geared steam locomotives that have been built have been for conventional track, relying on the adhesion between wheels and rail.
Henry Roe Campbell
One of the most visually striking features of a steam locomotive is its "wheel arrangement" which is largely a function of its intended application and purpose. The fundamental principle of design for 19th century steam locomotives was tractive force which relies on adhesion. A switching locomotive for example, is relatively low-powered but with a high starting tractive effort for getting heavy cars rolling quickly. These locomotives are geared to produce high torque but are restricted to low top speeds and have small diameter driving wheels. Switchers are rail analogs to tugboats. For higher speeds, larger boilers were required which in turn led to the development of lead trucks.
Prior to 1832, the typical locomotive for general road service on American roads was a 2-2-0 which could be built with either inside or outside steam cylinders. The critical element of the design was the single pair of driving wheels placed either in front of the firebox, as in the Norris engines, or in back of the firebox, as patented in 1834 by E. L. Miller and used extensively by in the Baldwin engines.