Given that 26" wheels have been so common since mountain bikes entered the market in the early 80s, I've always wondered: why 650c? Why didn't bike manufacturers just make a narrower version of the 26" wheel? For a while it was possible (maybe still is) to get 1.25" slicks for mountain bikes, how hard would it be to go just 1/4" narrower? Why introduce an almost-but-not-quite identical European size?