Time for a change.
Join Date: Jan 2004
Location: 6 miles inland from the coast of Sussex, in the South East of England
Bikes: Dale MT2000. Bianchi FS920 Kona Explosif. Giant TCR C. Boreas Ignis. Pinarello Fp Uno.
Why get technical. Measurements don't work because of so many factors. If it has a 58cm top tube- then it has a 58 cm top tube. By raising the saddle and bars by 2 or 4 cms- you can then adjust the seat or bar stem length to suit. You could be putting the seat as much as 7 cms further back- or further forward, and the same on the length of bar stem you fit. That can alter by 10cms if you wish it to.
So in reply to your question the only way -Unless you know where the saddle and bars are going to finish up in the fore and aft position- is to set the bike up and measure- but the top tube will still be 58cms.
Unless you get onto the bike guru on this forum and he disagrees- But I am certain that DG will come up with the same reply.
How long was I in the army? Five foot seven.