Originally Posted by Canker

Are any of the 10 speed RDs rated to handle a 42? I'm not going to look up specs but I don't think so. The one I'm running is an old as dirt X0 non-clutched mountain 10 speed which I'm am 99% sure is rated to max out at 36. Again the Sram 10 speed mountain RDs will generally work fine rated for it or not with a 42. Generally doesn't mean always it means most of the time. OP won't know for sure though until OP tries it. If OP is one of the really unlucky few that it won't work for then you can always go the roadlink route.