Shimano ultegra di2 6870 11 speed rear mechwith di2 technology shifting is easy and precise just a light touch as soft as a mouse click is sufficient for the front or rear derailleur to instantaneously select the correct gear programmed automatic motion at the touch of a switch makes this derailleur quick smooth and effortless to shift the removal of traditional mechanical cables in favour of electrical wires not only eliminates poor shifting caused by contaminates corrosion and stretchin