System efficiency continues to drive Shimano's innovation, and it's apparent in the new Deore 12-speed rear derailleur. Taking a quieter approach to trail sessions, Shimano uses Shadow RD technology, which stabilizes the chain to reduce slap, and more importantly, chain drop. With less tension in the low gear and optimized chain tension down the bloc, constant chain management leaves your drivetrain looking more like a well-functioning single speed than an oversaturated pasta noodle. The result also satisfies woodland animal's decibel-level ordinances as chain slap is dramatically reduced. The larger pulley with 13-teeth further increases efficiency, reduces noise, and affords faster and more precise shifts than previous generations. Optimized for 1 x 12 drivetrains and fitting up to Shimano's 51-tooth cog, this is a fully modernized and trail-eager derailleur.