Geared steam locomotive
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
Steam locomotive
The chassis, or locomotive frame, is the principal structure onto which the boiler is mounted and which incorporates the various elements of the running gear. The boiler is rigidly mounted on a "saddle" beneath the smokebox and in front of the boiler barrel, but the firebox at the rear is allowed to slide forward and backwards, to allow for expansion when hot.