Shimano

Ultegra RD-6700 Rear Derailleur

Wider links. That's the secret sauce for better, faster shifting at the rear derailleur for Shimano's Ultegra 6700 rear derailleur. Think about how wider things are better at resisting torsional load than narrower things. Same thing for the new Ultegra design. The shift plates are wider, connecting to the pivot and knuckle further apart, and thus better to resist flexing and twisting when you shift under load.

As always with Ultegra, this is a trickle-down design from Dura Ace. So, yes, it will work with 7900 shifters no problem. It will work with old Ultegra (6600 and SL) shifters no problem. The differences, however, are many. The obvious one is that the derailleur isn't as light. There's more metal and the pulley cage is made from composite plastic rather than carbon fiber. The pulleys are the same size as DA pulleys, but run on bushings, or in tech-speak, sleeve bearings. The cage design, along with the pulley cage placement, allows this derailleur to work with cogs as tall as 28 teeth, nice for those who want a really low low gear, and still a light derailleur and fast shifting.

The Ultegra rear derailleur is designed to work with 10-cog cassettes, though it will also work with nine-cog cassettes. The limit screws are on the back of the derailleur, just above the barrel-adjuster, and can be accessed from the rear.