Originally Posted by
mack_turtle
...that fit me just fine in original form. When I put a drop bar on them, they suddenly became waaaay too long no matter how high or short a stem I used. I am trying to avoid a repeat of those. When I did those experiments, I has the keys to a bike co-op, so I could go in any time and tinker. I no longer have that luxury.
There's nothing sudden about it. Nearly everything is known before you start a conversion. Drop bar specs (reach) are published on most bars. Sites like:
Stem Comparison Tool | yojimg.net
give you a specific idea of the impact a stem will have on stack and reach.
Stack and reach isn't published on vintage frames, but seat tube and top tube length usually is, as well as the frame angles. If you have a stack-reach range that you know fits you well, then the potential for a drop-bar conversion fit can be ballparked reasonably well. If no specs are available and you at least have a side photo of the bike, then you can use parts on the bike to make scale measurements of the tob tube and seat tube (example..the crank is most often 170mm..measure the crank arm and then use that to make scale measurements of anything else). The shorter headtubes on some bikes usually means some stem extension is needed. Longer exposed stem results in shorter (handlebar) reach..this can be estimated with the stem calculator above.
There are always some unknowns with how a converted bike will all feel in the end, but most of the mystery can be taken out before you start.
edit: I should have mentioned...in making estimates on how a conversion will go, you'll need to work with both the frame stack and reach as well as the handlebar/flat-bar stack and reach AND the potential drop bar stack and reach...the key is to put the new bars in the "space" that's comfortable for you to ride. That "space" can be calculated-estimated before you start.