The SRAM Red AXS E1 12-Speed Rear Derailleur the heart of the AXS ecosystem is lighter more efficient and more capable than ever. Covering cassette ranges from 10-28T up to 10-36T this wireless wonder has larger pulleys to decrease chain articulation and increase efficiency and an Orbit fluid damper to keep everything in place over the rough stuff. One derailleur ready for 1x or 2x on road or off.