Frame size.
 

How do you measure torso and arm lentgh for found the effective top tube. I have one groupset and wheels. Two of my road bikes one aluminum one is steel the aluminum is 58cm the top tube is 56cm. The steel bike is 56cm seat tube and 56cm top tube. I want upgrade one of that bikes and i try found what effective top tube is good for my height 5`7 feet and my inseam is 32"

With a tape Measure of Course.. that 32" include your Feet?

Im 5'9" & i like the RB1 I got in 1990, its a 56 with a 565 tt. I barely have a Fist width of seat posy Out.

If you have a sloping top tube frame the seat tube will be shorter .

how much clearance is there standing flat footed straddling the Top tube ..
lift up the front wheel how far can you get the tire off the ground?

you Will find a form to fill in on some Hand Made custom Frame Builder's sites ,
of course the analysis is part of actually Buying the Custom ..

maybe other I.T. young guys have a favorite site . ( graduated HS in 1966)