Shimano Index System: The system constituents such as the index mechanism built into the shifting lever, the frictionless SIS rear index shifting cable and the smooth action rear derailleur realise the Shimano Index System (SIS).
Double Servo: Shimano's double servo-panta mechanism enables the rear derailleur to move in an optimum path. The guide pulley tracks the cogs closely while moving front to back, optimising each shift. Perfect tracking contributes to the most accurate SIS shifting. Keeps rear derailleur guide pulley an optimum distance from each sprocket.