Sram x1 rear derailleur type 21 11 speedevery detail of the 11 speed x1 x horizon rear derailleur is engineered for smooth reliable shifting action from the larger upper pulley offset to the 12 tooth x sync pulley wheels by eliminating unwanted chain movement x horizon shifts faster puts an end to ghost shifting and reduces shift force and chain slap and with cage lock technology wheel removal and installation are easier than ever007518070000