[jean_claude]

>Well for adult bikes you are pretty much fixed at 700C. If making a bike pedaled contraption not so much.

For racing/road bikes, maybe. You're leaving out the 26" wheel adult bikes (which over time has encompassed 5 different rim diameters[1]) and 24" wheel bikes that are targeted at youth, but smaller adults sometimes prefer (well, those that have been give the option).

My bike pedaled contraption is a rear suspension compact long wheelbase recumbent with two real 20" (406mm rim) tires and they're spectacular.

[1] http://www.sheldonbrown.com/26.html

[brianwawok]

I feel like less and less bikes are going for 26s. It used to be that the smallest bike or so from each manufacturer used 650C, then everything else used 700C. Seems like most manufactures just went to 700C for all adult bikes over the last few years...