My method for getting in the ballpark for frame size is the Greg LeMond/Cyrille Guimard method. Using a virtual TT, measure frame size (C to C) in CM. If your inseam (in socks) in CM is multiplied by .665 it should give you a size that is ballpark. From there it's a matter of what feels best for you. I have a 32.25" inseam and can ride anything from 54-58. My best fitting bike is my Guru Sidero and that's a 55 with a 55 TT. I also am comfortable on my 58 Masi but the Guru is perfect.