Grain loss due to combine header comprised more than 50% of the entire harvesting losses. This study was performed to determine the best adjustments of the combine header components for reducing the gathering loss using combine "Claas Lexion-510" in Iran. The adjustable factors influencing combine header losses were forward speed, peripheral reel speed, cutting height, horizontal distance of reel tine bar from cutter bar and vertical distance of reel tine bar from cutter bar. The Taguchi method was utilized for the design and analysis of the experiment. A total of 54 experimental runs were conducted using an L18 orthogonal array. Results showed that the best combinations of setting parameters were level 2 for the forward speed (2.5 km/h), level 2 for the peripheral reel speed (3 km/h), level 2 for the cutting height (30 cm), level 3 for the horizontal distance of reel tine bar from cutter bar (10 cm) and level 1 for the vertical distance of reel tine bar from cutter bar (5 cm), which resulted in the minimum gathering loss. Furthermore, the forward speed had the highest effect on gathering loss and cutting height, peripheral reel speed, vertical distance of reel tine bar from cutter bar and horizontal distance of reel tine bar from cutter bar were arranged in the lower ranks, respectively.
