Much like how the XX1 rear derailleur originally began as a product for the DH world, the group's X-Sync chain rings also have roots in another realm: touring. The story goes that a unorthodox chain ring was developed for cycle touring that employed radically shaped teeth designed to hold the chain onto the ring as the bike was being ridden over rough roads, thereby keeping the casual cyclist from having to get themselves covered in grease when reinstalling the chain. Although XX1 uses the same concept, the idea has been taken to the next level. The design uses alternating tooth profiles; one with a thicker and heavily stepped shape, followed by a more standard looking tooth. When viewed from above, the alternating teeth match the inner profile of the male and female chain links. The radical teeth work with the XX1-specific chain to limit the chance of it lifting up and off of the ring. Size options will include 28, 30, 32, 34, and 36 tooth rings, although odd tooth ring sizes will not be available due to the alternating pattern of the X-Sync design.

They do however recommend a guide for anything really gnarly don't they?

Although XXI is all new, the only parts that seem to eliminate the need for a chain guide are the dampered mech and the chainring