I agree with Jaka, make the wires as loose as you can and still get control. Make sure that you have a bit of what many call Akerman(spelling) installed. That is where the cable not being pulled actually slacks of a slight bit when the other cable is pulled. You do this by having the points where the cable attaches to the rudder horn very slightly ahead (forward) of the hinge line on the rudder. You can also do this by having the attach points of the control horn on the servo slightly ahead (forward) of the center of the servo arm pivot point.