Originally Posted by Kontact

Tire size and wheel size are mainly relevant because we're mainly talking about racing bikes, and racing bikes are supposed to be more alike than different. Which allows them to receive neutral support wheels and that sort of thing. No one frets about tire size with MTBs or recumbents because there isn't that history and group rides don't happen the same way. There is no reason not to use 650c wheels if you want to, but it is understandable that people don't feel like they quite fit their conception of road bike. They also seem to work fine down to 5'2" if the bike is designed well.