Sram x01 dh type 21 10 speed rear mechsrams dh specific derailleur is designed to provide fast and precise shifts for the close ratio cassettes used on dh race bikes 4x and jump bikes x horizon architecture provides more responsive shiftingx actuation with more cable pull provides better system performance and durabilityx horizon eliminates ghost shifting very commonly found on dh bikesexact actuation mtb 10 speed variant allows upgrade to existing bikes in the aftermarketx sync a cnc mac