The drawbar pull characteristics of small size tractors with four-wheel drive
(4WD) and two-wheel drive (2WD) were evaluated on asphalt pavement and a test
field by Martia et al. [10]. On asphalt pavement the maximum drawbar force was obtained in second gear. The drawbar force of the 4WD drive tractor was 1.4 times
greater than that of 2WD tractors on asphalt pavement and 1.6 times on the test
field. Wheel slippage in 4WD mode was much smaller than that in 2WD mode on
asphalt pavement and test field. When wheel slippage was the same, the drawbar
force of the 4WD mode was twice that of 2WD mode on asphalt pavement and
2.3 times greater in field tests