Actual speed of an articulated-frame wheel-skidder of full-tree skidding was investigated. Uphill speed with no load was affected by the grade, i. e.: the higher the grade, the lower the speed. The speed was about 6 km/hr when the gradient was 6°〜13°. The previous day's rain caused much slipping of tires at a section of 11°. The curves did not affect the speed because of the tractor's small turning radius. Even when the radius of curve R was 8m, the decrease of the speed against a straight course of the same gradient was only about 1km/hr. Downhill speed of straight courses with logs of less than 4.6m^3 varied over a range of 2.6〜14km/hr when the gradient was less than about -7°. When the gradient became -6°〜-13°, the speed was 4〜7 km/hr with a payload of 2.4〜4.6 m^3. The speed of lifting the small ends was lower than that of lifting the butt ends. Downhill speed with load was much affected by the radii of curves. For example, when the grade was about -11° and R was 30 m, the speed decreased to 3.5〜5.5 km/hr, whereas the speed on a straight slope was 4.5〜7.4 km/hr. When R=8m, the speed decreased to 2.2〜3.6 km/hr. Even when the gradient was only -5.5° and the R=20m, the speed of the skidder was affected negatively by the radius of curve. The above results can be used to design a skid road for full-tree skidding.
