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
More-powerful locomotives tend to be longer, but long rigid-framed designs are impractical for the tight curves frequently found on narrow-gauge railways. Various designs for articulated locomotives were developed to overcome this problem. The Mallet and the Garratt were the two most popular, both using a single boiler and two engines (sets of cylinders and driving wheels). The Garratt has two power bogies, whereas the Mallet has one. There were also a few examples of triplex locomotives that had a third engine under the tender. Both the front and tender engines were low-pressure compounded, though they could be operated simple (high-pressure) for starting off. Other less common variations included the Fairlie locomotive, which had two boilers back-to-back on a common frame, with two separate power bogies.