Originally Posted by luker

The size of the headtube has a relationship to the size of the bike. There are other factors, like whether the bike is built for fender clearance, and which type and size of wheel will be installed, but in general, the longer headtube goes with a longer seat tube, and the seat tube grows longer with larger bikes...Mountain Biking this month has an 80cm bike built for the Chinese guy that plays ball for Houston. The seat is just about as tall as I am.