A tractor-pull sled design refers to a plan for the metal sled, also known as a sledge, that is drawn by tractors along a prescribed track in the sport known as tractor pulling, truck pulling or power pulling. Sled designs have been growing in complexity as the tractors that pull them become increasingly powerful.
Tractor pulling traces its origins to 19th-century farm contests in which a barn door laid flat on the ground acted as a sled and was dragged around a farm by a horse. People stood at fixed positions and stepped onto the door as it passed. This was done until the weight became too much for the animal. The horse that pulled around the largest number of people won.
Horses were displaced by motorized vehicles in 1929. However, the sport didn't really catch on until the '50s and '60s. In 1969, a National Tractor Pullers Association was formed to create a single set of nationwide standards from the confusing patchwork of rules that varied from state to state. At that time, sleds still utilized the step-on method or were made out of a heavy block of steel. However, this changed as tractors became more powerful.
Modern sleds utilize a system of gears to gradually move heavy weights from the rear to the front axle as they are pulled around a track. This pushes the front end of the sled to the ground, making it increasingly difficult to pull. The tractor that drags the sled the farthest wins.