Understanding geometry...
Hello All,
As I have learned more and more over the years about how my bike fits, I have studied various geometry charts and think I've realized a major omission from various manufacturers' charts. Correct me if I am wrong, but isn't horizontal offset from the BB more important than top tube dimensions. Colnago and Pinarello include it from the seattube and Cervelo from the headtube, but Bianchi doesn't, Giant doesn't, Cannondale doesn't, Specialized doesn't, Merlin doesn't, Litespeed doesn't, Scott doesn't to name a few.
I have bikes that have varying top tubes from 55 to 56.5 and their "cockpit", how Cervelo describes the BB to head tube dimension, differ by only .6.
For example, Colnago 56, 57 and 58 sized bikes have a top tube dimension of 55, 55.6 and 56.3 respectively. But their cockpit dimension, i.e. the top tube dimension minus the published setback dimension, are 39.7, 39.5 and 39.9. I take this to mean that the 57 is actually the "smaller" bike. It would require a further setback saddle or a slightly longer stem to maintain the same position.
I just thought it was intereseting, because I used to look at top tube dimension for my purchases, but no realize that may vary your relationship to the BB.
Is my understanding right, and is it incorrect to size based on top tube dimensions?