Originally Posted by
Young Version
I believe you're being willfully obtuse here. It is common knowledge that the most important measurement in fitting the right size frame is ETT. When a company says their bike "fits like a 54cm", they mean that's the closest nominal ETT, not ST. Do a search on eBay for 54cm bikes and see how many with sloping geometry are referring to the seat tube.
We discuss sizing based on ETT length to avoid this exact conversation, because everyone knows that nowadays ST length is almost meaningless. I ride a "50cm" Ridley, but it's really a 53cm top tube. My Wilier has a 54cm top tube and a 48cm or so seat tube--I would obviously call this a 54cm bike, not a 48cm.
The size sticker on the seat tube, when it has a number rather than a s/m/l letter, usually refers to an "effective" seat tube length. That's not always true, though. Some manufacturers use actual seat tube length, even with a sloping top tube. And there's still the small matter of whether the effective length is c-c or c-t. It's best not to pretend there's any applicability of any "frame size" number across manufacturers.
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