Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Engineering Science (Interdepartmental Program)

First Advisor

Malcolm E. Wright


A machine was built to study non-rolling tire stiffness and damping coefficients of agricultural tractor tires in the vertical direction. Static deflection on a rigid surface was measured as a function of vertical load. During dynamic experiments, a sinusoidal forcing function was imposed on the test tire to determine dynamic stiffness and damping coefficient from load and deflection measurements. The experimental setup and methodology are described. Ten tires were tested. Both static and dynamic stiffnesses appeared linearly related to inflation pressure. No correlation was found between dynamic properties and excitation frequency. Comparisons among stiffness and damping coefficient values were made according to section width, carcass construction, and between tires of the same size. Traction tests were made at the National Soil Dynamics Laboratory, Auburn, Alabama. Four tires (14.9-30, 14.9R30, 18.4-38 and 18.4R38) were tested on Norfolk Sandy Loam after measuring their rolling radius on concrete under self-propelled condition, at three levels of inflation pressure, and under varying load. Traction experiments were made at three levels of inflation pressure, two levels of longitudinal slip (7.5 and 15%) and under varying dynamic load for each tire. Slip, carcass construction and inflation pressure significantly affected the pull ratios. A mathematical model is proposed that accounts for effects of tire inflation pressure and dynamic load on rolling radius.