Shimano calls it "Shadow Plus" and first introduced the technology in 2012 with the Shimano XTR, while Sram followed suit in 2013 with its "Type 2" technology for the XX1, X0 and X9. Both systems ensure that the lower derailleur arm does not swing as much while riding, preventing the chain from hitting the frame or even jumping off completely. But how do the systems actually work? And do they make a chain guide unnecessary?
The functional principle of both systems is basically the same: the preload is increased via an additional spring mechanism in the lower joint of the derailleur arm. This increases the resistance in the joint and a higher force counteracts the movement of the arm, which would otherwise rotate forwards against the direction of travel in the event of vibrations. Reduced chain tension as well as the chain hitting and jumping off are prevented by the higher pre-tension of the derailleur arm. And this is achieved without significantly increasing the operating forces of the derailleur. The technologies are available for almost all common gear systems.
And does it work? Yes. Both systems reliably prevent the big rattles. The chain also stays on the chainrings for much longer, meaning that a separate chain guide is unnecessary for many in classic touring use. However, it is not possible to completely prevent the chain from jumping off even with a "stabilised" drive.
Shimano's Shadow Plus function can be deactivated via a small lever on the rear derailleur. However, there is no reason for this when riding, but it does make it easier to remove the wheels. The Sram Type 2 system is permanently active. The rear derailleur arm can be locked in the front position for easy removal of the wheel. To do this, move the arm forwards and press the locking button with the lock symbol (Sram calls it "Cage Lock"), which locks the derailleur cage. To unlock, simply turn the cage forwards again until the button pops out automatically.
