This study investigated the potential use of wide skidder tires for forest harvesting operations on steep slopes. During the summer of 1984, field tests were conducted to compare the performance characteristics of 24.5-32 and 66-43 rubber tires on a JD-640 grapple skidder loaded with tree length material. The skidder was operated on 20%, 25% and 30% slopes on Piedmont soils near Rome, Georgia. Video recorders were used to document the field measurements and observations of machine travel time and wheel slip over defined courses. Soil compaction was evaluated by comparing soil cone penetrometer readings taken in the wheel tracks of the test lanes to those taken in undisturbed adjacent areas. Skidder lateral stability was analyzed using the mathematical model developed in this study. Based on the results of statistical analyses of the data and field observations obtained under the test conditions, the skidder equipped with wide tires generally attained higher average speeds, tended to cause less wheel slip, resulted in smaller increases in soil cone penetrometer readings, and had significantly greater stability on sideslopes than the skidder equipped with the narrow tires. The stability model developed in this study predicted the critical sideways tipping angle for a JDâ 64O grapple skidder to be approximately 32° when fitted with the 24.5-32 tires, and 44° when fitted with the 66-43 tires. / Master of Science