Development (North America)
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.
The steam engine was gradually phased out by the mid-1920s as the less expensive, lighter, and faster-starting internal combustion (kerosene, petrol or distillate) tractors fully emerged after World War I.
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