ABSTRACT THE effects of tire size, inflation pressure, and percent travel reduction on bulk density were determined on ourdoor bins filled with soil from the lower Ap horizon of the Cecil, Hiwassee, and Lakeland soil series. The single-wheel tire tester of the National Tillage Machinery Laboratory at Auburn, Alabama, were used in the tests. The three skidder tires used in the study were a 10 ply 18.4-34, a 12 ply 24.5-32, and a 12 ply 30.5L-32. Travel reduction (percent slip) had a greater influence on soil compaction than tire size or inflation pressure. The higher travel reduction level (30%) was associated with a decrease in soil compaction. Dynamic loads beyond about 20 kN did not cause additional increases in soil compaction.