Originally Posted by bostontrevor

700c is bigger than 26", but what it translates to is completely use (and tire) dependent. The real thing is that a traditional 26" mountain bike rim has a 559mm (22") diameter. Add a 2" tire and it gets to 26". Of course the classic mtb tire is actually 1.75" and that actually leaves us 1/2" short of 26", but talking about a 25-1/2" wheel is inconvenient.

700c comes from French sizing. Match a true 700C tire with a 700C rim and you'd have a 700mm wheel. The rim itself is 622mm. These days 700c means nothing more than a rim or tire designed around a 622mm bead diameter.

Put a 700c rim on a mountain bike and you have what's commonly known as a 29" wheel because--you guessed it--add a 2.3" tire to a 700c rim and it works out to about 29".

Your classic 27" road bike wheel is a 630mm rim designed for a 1" or 1-1/4" tire.