Originally Posted by chaadster

I was responding to the comment that one wouldn't expect much seat post extension on a level TT bike, not comparing seat tube lengths.

I certainly understood rpenmanparker's comment in the context of traditional bike frame design, and don't disagree with him on that count, but my point was to remind that our notions of proper fit are largely predicated on changeable and variable attributes of frame design. Sure, traditional diamond frames may have been "square" (i.e. of same length ST and TT), but there's nothing about sloping or level TTs to prevent a 54cm ST frame's TT from being the same length as a 57cm ST frame's TT, or even from being longer. For example, a Torella Corsa Strada 54cm has a 545mm (level) ETT, while a the Surly Cross Check 54cm has a 560mm (level) ETT, and the new Breezer Venturi with a 54cm ST has a 570mm (slightly sloping) ETT.

So the point in all this is not to cavalierly toss around frame sizes, because that doesn't tell us anything, and certainly noting whether a top tube is level or otherwise tells us even less (and nothing about seat post extension, which has only to do with the height of the rider vis a vis the top of the seat tube).