Shimano's Dyna-Sys11 MTB jockey wheel set includes sealed bearings on both wheels for easy and low-friction operation.
Dyna-Sys11 The real advantage of an 11-speed drive train is the ability to have all the range you require without sacrificing the rhythm you need. DYNA-SYS11 maximizes rhythm with “rhythm step” gears in the most frequently used range. Drive efficiency is a key performance indicator for the drivetrain. Dyna-Sys11 means more speed with the same effort.