When farm machines are operated in the field or on the road at speeds higher than 2 1/2 to 3 miles per hour they should be equipped with rubber tires. And when these machines are pulled behind rubber-tired tractors the speed should be as high as the operating conditions and the design of the machines permit. In most cases the speed will be higher than 2 1/2 to 3 miles per hour for most efficient use.
McKibben, Eugene G. and Davidson, J. Brownlee
"Rubber Tires Lead!,"
Farm Science Reporter: Vol. 2
, Article 3.
Available at: http://lib.dr.iastate.edu/farmsciencereporter/vol2/iss2/3