Shimano's Ultegra Rear Derailleur delivers category-defining 11-speed shifting. At the heart of the derailleur is a light, tough, cold-forged-aluminum body with a wide, rigid pivot design that maximizes shifting speed and equalizes shift effort across the cassette. Smooth-spinning pulleys use sealed bearing to keep out the dirt and ensure quiet running in the miles to come.
An important part of a rear derailleur's job is keeping the chain taut as you change gears. Chain-wrap capacity is a number that tells whether or not a derailleur will be able to do this on the drivetrain you plan to use it on. Calculate chain-wrap capacity with this formula: Chain-wrap capacity = (large chainring - small chainring) + (large rear cog - small rear cog). Example: 44/29 chainrings and a 11-28 cassette: (44 - 29 = 15) + (28 - 11 = 17) = 32-tooth chain-wrap capacity.