This derailleur provides efficient, smooth and precise shifting across standard and wide ratio cassettes, providing exceptional shifting performance.  Shimano Shadow RD Derailleur Technology The addition of Shadow RD Road technology ensures that the derailleur sits low-profile against the bike chainstay. It features a single-tension design so that the derailleur will be stable and not hit the chainstay when in rough terrain conditions and it also restricts chain slap and rattling when riding; it provides silent and super-smooth performance.