oil is a non-renewable and valuable resource, which needs to be sustainably managed. Therrfore, its physical degradation by erosion and compactio should be prevented. Soil compaction depends on tractor parameters (axle load, ground pressure, tire inflation pressure, type and size of tire, tire configuration, tractor speed and traffic frquency) as well as soil characteristics (structure, texture, bulk density, water content (WC), clay content and organic compounds). The objectives of this research were: a) to study the relationship between tire sinkage ( and soil bulk density (BD), qusai-static soil resistance (CI) and dynamic soil resistance (DCI), b) to determine precompaction stress ( ) and compression index ( ) (using plate sinkage test (PST) and confined compression test (CCT) and c) to determine the relationship between the tire sinkage ( ) and the precompaction stress under different soil WCs. Treatments included three traffic frequencies (0, 1, 2 and 3 passes) with two tractor types (MF285 and MF6290) at two soil conditions (plowed and unplowed) and under different soil WCs(0.9PL, PL and 1.1PL; PL =Plastic Limit) in a clay loam soil. The research was conducted at the Agricultural Research Farm, Isfahan University of Technology. Variables measured were: CI, DCI, BD,,, . The CI, DCI and were measured simultaneously along the tire centerline within the wheel track and the soil samples for WC and BD measurements were also collected around the same point The Values of and were determined on large undisturbed soil specimens collected from the wheel track and measured with two different methods (CCT and PST). The stress-sinkage and stress-strain curves were drawn for both PST and CCT, respectively. Three different methods were used to