When the tractor is used on a side slope field or travels along a curved path, the side force exists on the tires and it is useful to keep the steering stability of tractor.
A theoretical study of the development of the side force at small side slip angle on automobile tire was published by E. Fiala. In this paper, the applicability of its theory to the side force at any side slip angle between 0゜and 90゜on the tractor tires was investigated using the apparatus of two wheel cart.
Main results are as follows :
(1) The maximum value of side force S_m = μW is obtained at the side slip angle β_m shown by the formula,
β_m = <tan>^<-1>(3μ/C_2)
where W is weight of tractor, μ is coefficient of friction, and C_2 is factor of cornering coefficient.
(2) The relation between side force S and side slip angle β is assumed as follows :
When 0゜≦β＜β_m, the value of side force is
S = (C_2 tan β - (C^2_2)/(3μ)<tan>^2 β + (C^3_2)/(27μ^2) <tan>^3 β) W
When β_m≦β＜90゜, S = S_m.
Using the chi-square criterion, the hypothesis, that the side force calculated on the base of these assumptions is equal to the testing value, is accepted at a level of 0.01.
(3) From these results, C_2 = 1.75～3.53, μ = 0.63～0.71, and rolluing resistance R = 0.043～0.086 on the concrete road were calculated.