For the purpose of establishing the running theory of tractor on the slope field, we studied on the side slip angle of the pneumatic tire using the running locus of model tractor given the right angled side force P_s against its center line.
The term K = P_s/ W/β decreases with the larger pull value of P, where W is the weight of the tractor and β is the side slip angle of tire. But at the range of P_s/W = 0.3-0.4, under the constant value of P, K is maximum value, and on that case it may be possible that tractor has smaller slippage. This is due to the improvement of the adhesion of the tire to the land surface. On the another aspect, it shows that this character gives only few influence for the tractor under the small values of P and P_s.
On the effect to β by the values of P and P_s, β is influenced by the value of P_s under the small value of P, and by the value of P rather than the value of P_s under the large value of P. On the case of the large values of P and P_s on both, the effect becomes larger and the value of β increases rapidly.
Side slip angle α, deflection angle which we have called in our study up to this time letting the tractor run along the contour line on the slope field, is larger value comparing with the value of β. But by the converting the past result into the test condition stated above, using the equation (12) under the condition of same slippage, we get nearly the same side slip angle β = α, where S_<p(n)> and P_c are the side force and pulling force of the running tractor along the contour line.