As it has been explained to me, the most important factor in determining proper bike fit is nailing down the correct top tube length. It has also been explained that the measurement that yields top tube length is a person’s torso length. Assuming the above information is correct, what has not been explained to me is how the torso length is “converted” into proper top tube length. Would a 52 cm torso (as measured from center of hips to center of shoulders) translate into a 52 cm top tube or is there an acceptable range for figuring such?
In the meantime, take your existing bike, assuming you have clip-ons and are riding somewhat similar to the way you’d set up the new bike. figure out the relation of the saddle to the BB (relative seat angle calc’s found on this forum) then measure the distance to your bars (on a flat plane, not sloping down from the saddle). Now adjust for anything you don’t like about your present setup (reaching too far, too cramped). Do the same for whatever bike you’re interested in (taking an educated guess about where you’d want the saddle). If you’re off by a cm or two you can cover that with a stem. If you’re using a stem below a 100 then make sure you can find a stem you like. Many companies seem to be not making 90’s anymore, and finding stuff under a 90 is tough. Syntace has 90’s and 75’s, Thomson makes shorties in their mtn stems (their beautiful and well made, but kinda chunky for a lithe TT bike).
If you don’t have a bike to work with now, then I guess you can wait for the mathmaticians, or real fit experts to show up.
Ritchey still produces its beautiful WCS and Pro road stems down to 80.
Dig around slowtwitch. Dan has written vast amount on this very topic. In fitting friends, I always start with Dan’s formulas and they have yet to fail.