Originally Posted by TimArchy
Unless one is looking at a custom frame (and I don't believe we are), geometry actually does change as the size (generally taken from the seat tube length) changes. If you define the term "to require" as something to which you have no alternative, than a change in geometry is generally required when changing sizes.
This is simply the way mass production frames are made. You should have noticed this when you were purchasing your crosscheck.
Yes on most modern bikes they do, because when you change tt length(NOT ST LENGTH) you need to change some other aspects of geometry to make everything work right. Further, tall people may not be shaped like short people so some designers will try to accomodate that one way or another. His comment about a ST/TT ratio determining something meaningful about the rest of the geometry was completely wrong. Look at old road bikes if you don't believe me. Many are built with nothing varying across the sizes other the ST and HT.