Ultegra Shadow design with 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 Features: Sleek and low-profile Shadow design reduces crash risk. Switch-operated automatic motion ensures quick, smooth shifting. Electrical wires replace traditional cables, preventing shifting issues from contamination, corrosion, and stretching. The derailleur includes a saver function to protect it from strong impacts. Constructed with high-tolerance cold-forged aluminum for durability and lightness. Four self-lubricating fluorine-coated pivot bushings ensure smooth shifting with low friction. Compatible with 11-speed E-tube Di2 systems. SS (Short cage) Wide gear ratio compatible with 11-25 up to 11-30T GS (medium cage) Wide gear ratio compatible with 11-28 up to 11-34T