Abstract. One of the important considerations of soil-tire interaction research is the stress distribution in the topsoil and within the cultivated soil volume due to tires. This stress distribution influences trafficability, ride performance, and tractive performance. In this study, a two-wheel-drive tractor and a group of piezoelectric pressure sensors were used at different tire loads and inflation pressures to (1) measure the vertical stress under three tire loads with three inflation pressures and determine the influence of these two parameters on the vertical stress in the topsoil, as measured by sensors with their upper surfaces at an initial depth of 50 mm within the soil volume; (2) develop an empirical relationship between the vertical stress and the depth beneath the soil surface, the tire load, the inflation pressure, and the lateral sensor distance from the tire centerline using multiple linear regression; and (3) analyze the effects of tire load and inflation pressure on vertical stress to contribute to the understanding of soil compaction processes based on the equation we developed. All vertical stress measurements were conducted when traffic was applied to the soil by the left front tire of the tractor, with forward motion of the tractor stopped before the left rear tire reached the sensors. The results indicated that (1) when the inflation pressure decreased, the soil-tire interface stress curve became smooth and the peak value of stress gradually moved to a point near the edge of the tire, whereas when the inflation pressure was higher, the peak stress value occurred in the center of the tire; (2) low inflation pressure significantly reduced the maximum vertical stress; (3) the vertical stress was influenced by all four factors investigated in this study; and (4) the stress within the soil volume varied as a quadratic function of the inflation pressure at a given tire load, and it varied as a linear function of tire load at a given inflation pressure. Keywords: Stress distribution, Tire load, Tire inflation pressure.