Just by looking at the frames, what jumped out at me is that the 650b version has a sloping top tube. The geometry charts that @J.C. Koto linked to will show the differences in more detail. I'm curious if anyone else can weigh in on how those differences affect the ride? I've been interested in the Straggler for a while but was concerned that the original frame wouldn't fit me well (5'4" woman). The new 650b frame looks promising, but I don't know enough about bike geometry to understand what is at stake in the changes.