Steam tractor

A steam tractor is a vehicle powered by a steam engine which is used for pulling.

In North America, the term steam tractor usually refers to a type of agricultural tractor powered by a steam engine, used extensively in the late 19th and early 20th centuries.

In Great Britain, the term steam tractor is more usually applied to the smallest models of traction engine - typically those weighing seven tons or less - used for hauling small loads on public roads. Although known as light steam tractors, these engines are generally just smaller versions of the 'road locomotive'.

This article concentrates on the steam-powered agricultural vehicles intended for the direct-pulling of ploughs and other implements (as opposed to cable-hauling).

Owing to differences in soil conditions, the development of steam-powered agricultural machines differed considerably on either side of the Atlantic.

In Great Britain, a number of traction engine builders attempted to produce a design of agricultural engine that could pull a plough directly, in place of a team of horses. However, the heavier and wetter soils found in Britain meant that these designs were not successful — being less economical to use than the team of horses they were intended to replace. These engines were also known as "steam tractors". Instead, farmers resorted to cable-hauled ploughing using ploughing engines.

A distinctive example of a British-designed (agricultural) steam tractor is the Garrett Suffolk Punch, a 1917 design intended to compete directly with internal combustion-powered alternatives.

The first steam tractors that were designed specifically for agricultural uses were portable engines built on skids or on wheels and transported to the work area using horses. Later models used the power of the steam engine itself to power a drive train to move the machine and were first known as "traction drive" engines which eventually was shortened to "tractor". These drive mechanisms were one of three types: chain, shaft, and open pinion. The open pinion became the most popular design due to its strength. Later improvements included power steering, differentials, compounded engines, and butt-strap boiler design.

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