The electronic Shimano Ultegra Di2 RD-R8050 rear derailleur is characterised by its particularly low profile, known as Shadow Design, which not only provides a compact appearance, but also more stability and less risk of damage. This guarantees quiet, safe shifting operations under all circumstances. Shifting takes place effortlessly as is usual with Di2. You can also use the Synchro Shift function, which allows the front derailleur to adjust automatically, or the Semi Synchro Shift function. This causes the rear derailleur to shift accordingly when the front derailleur is operated. The new direct mount option is also perfect for frames with thru axle dropouts. The Ultegra Di2 rear derailleur is mainly made of aluminium and is available in two versions: one with a short cage (SS type) for cassettes up to 11-30 and the other with a longer cage (GS type) for cassettes up to a gradation of 11-34. So you can enjoy even the steepest climbs of a smooth ride. Shimano Ultegra Di2 Rd- R8050 Rear Derailleur  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 Sleek appearance with Low profile Shadow design construction reduces risk of damage in a crash 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 stretching, but provides effortless gear shifts Derailleur contains a saver (fuse) function, where the inner structure is protected from strong impacts High tolerance cold forged aluminium link plates and body construction is extremely light and durable Four self-lubricating micro-machined fluorine-coated link pivot bushings provide low-friction shifting 11-speed E-tube Di2 compatible Wide gear ratio compatible with 11-25 up to 11-30T