Originally Posted by
wschruba
It's driven by an industry who can't decide how they want to market things, so generally speaking, inches refer to mountain bikes, French sizing to everything else.
This.
When they call a rim 29-er, they're marketing it to mountain bikers, and 700c, to roadies. They're the same diameter. The important differences are the width (which can vary through a pretty wide range, according to intended use), and the rim's shape, material, etc. I wish all manufacturers and all cycling disciplines would go to a universal sizing standard, preferably ETRTO.