bike sizing?

[Concept_3]

If frame sizes are defined by the length of the seat tube does this mean one would need different size frames for traditional road bikes, with level top tubes when compared to a modern sloping tube frame which would be different again from a TT bike?

 

[neuroportal]

Frame sizing - there are many theories but most people who ride a lot end up 'knowing' what fits them. Or spends a lot of money on Osteopaths etc.

However, this should help: http://www.sheldonbrown.com/frame-sizing.html

The length of reach, or from the seattube to the headtube along the crossbar, that is probably more vital for you than the seattube length. You can raise or lower a seat, you cannot as easily adjust reach. Yes you can slide your seat forward/backward and/or change your stem but not as easy.