Drawbar pull performance of tractors based on Italian type-approval data (1960-1989)

An analysis of tractor maximum drawbar pull is reported based on Italian type-approval tests for the period 1960-1989. Only for four-wheel drive (4WD) tractors has the vehicle traction ratio (ratio between maximum drawbar pull and gross weight) improved over the years. The 4WD tractors present the highest traction ratio among all of the wheeled tractors and, when used without ballast, have a value which is 3% higher than analogous front-wheel auxiliary drive (FWAD) tractors in the four-wheel drive mode. The FWAD tractors in the four-wheel drive mode and without ballast have a traction ratio which is 28% higher than when they are used in the two-wheel drive mode. The two-wheel drive (2WD) tractors without ballast have a traction ratio which is 8% higher than that of FWAD tractors in the two-wheel drive mode. The ballast does not seem to improve the traction ratio of FWAD and 2WD tractors, even if it increases, as would be expected, the maximum exertable pull. Typical traction ratio values for wheeled tractors on concrete and without ballast are 0.887 for 4WD tractors, 0.860 for FWAD tractors in the four-wheel drive mode, 0.723 for 2WD tractors and 0.672 for FWAD tractors in the two-wheel drive mode. Crawler tractors on level and compact farm-land and without ballast present a mean traction ratio of 0.917. (C) 1998 Silsoe Research Institute.