Ambiguous Frame Size is Ambiguous
 

So I have recently found out my frames are not ~54cm, but 56cm top tube length for my road bike and ~58cm top tube length for my fixed gear. Yup. Well, you learn something new almost everyday.

Why do you think bike manufacturers come up with crazy ways on measuring a frame? It seems ambiguous and inconspicuous if that measurement is referring to seat tube length from the bottom bracket to the top of the seat post or the top tube length. Isn't the top tube length the most important when considering a frame's size? Then follows the stand over height? Or am I missing something...

Forget about frame size. Read the geometry chart carefully before you buy.

Just different ways to measure. Yes, in general top tube length is the more critical measurement but even that can be substituted some by stem length. Seat tube length is measured both ways - center to center and center to top, depending on the mfg. Just the way it is.

Dude, bikes are built all over the world; different time zones throw off measurement schemes. Haven't we been over this?