I converted my twinn to a "6 speed" by replacing the cranks with modern square tapers, bmx conversion bottom brackets, a down tube shifter and a new rear wheel with a 6 speed cog. It works great and was a much cheaper (for me) option to the nexus. At the time of the build, I was told by several sources that the nexus would fail under load. After reading this I don't know... sounds like the nexus would hold up. I just wanted to make this alternative suggestion, it don't look as pretty, but it rides like a champ!