What are you riding? An F4i is supposed to have about 1-3/8" slack in the chain measured at the midpoint of the chain on the bottom. Just adjust till you get it, and check periodically to see if it needs to be adjusted, be careful not to overtighten it, also make sure you adjust the opposite side to the exact same spot as the chain side so the wheel runs true, double check your slack, roll the bike around some and check it again. You should also use a torque wrench when tightening the rear axle bolt after you get it where you want it.