The shimano zee m640 10 speed shdow design rear derailleur shimano39s new zee shadow rear derailleur reduces chain slapping and dropping thanks to the chain stabiliser system shimano zee m640 10 speed shdow design rear derailleur features shimano39s new zee shadow rear derailleur reduces chain slapping and dropping thanks to the chain stabiliser system 10 speed dyna sys compatible only low profile skid plate design 23 28t