The derailleur of the DURA-ACE R9100 series maintains its compact and smooth design. It allows for quick and smooth shifting under high pedal torque. Synchronized Shift enables more efficient gear changes while riding. This function offers numerous advantages, such as faster, more precise shifting under all riding conditions and minimizes the strain on the drivetrain. When Synchronized Shift is activated, the derailleur and front derailleur can be controlled with just one switch. With Synchronized Shift fully enabled, the derailleur detects the position of the rear derailleur and automatically shifts to the most efficient gear with the best chain line, so you no longer have to worry about shifting in the front or compensatory shifts. With the Semi-Synchronized Shift function activated, you can manually shift the front derailleur, giving you optimal control over selecting the best gear combination for your riding style. The system automatically makes the necessary corrections by shifting to the correct rear gear with the best chain line.