This may seem a naive question asked from the point of view of a consumer not a designer-builder. I\u2019ve been following this discussion and I keep wondering why the seat tube measurement is relevant at all if the ultimate goal is a particular standover height of the top of the top tube to fit a riders crotch measurement from the ground, or whatever height has been found comfortable from experience. Why would a measurement from the ground to the top of the top tube not be a more meaningful measure with which to state frame size? Are frames designed working backward from a desired height above ground, factoring in wheel with tire diameter, fork dimensions, desired bottom bracket to ground, etc. to arrive at the desired height? With a slanted top tube it would seem that a virtual top tube would have to be assumed for determining size. Why then would it matter what the seat tube dimension was or was called.
Sages have said that there are no dumb questions, only dumb answers. I ask in ignorance and hope to be enlightened.
George Jones Dallas, TX