Was in Grand Cayman last spring, but did not ride. The roads are excellent, since they are all brand new (hurricane upside?) and the island is quite flat. However, lighting is not great on the East Side at night. Cayman Brac has a hill and people rent bikes out there, but it's a pretty small island overall and not sure the roads are much - very little traffic though. You would have to get your bike on the little prop plane to get it over there.