I want to buy a frameset and built it up myself. So I am looking on ebay and elsewhere trying to find a frame. What makes me the most nervous is fit. I have tried a bunch of calculators out there to try to get a sense of what might be right for me. I have started to understand the significance of different measurements like reach and stack, etc. And I have tried to look at frames themselves and intuitively try to understand what a certain frame might feel like. But give my lack of experience these efforts seem as though they will remain approximate. I know that I could go to a bike fitter but I think this is a risk I cannot take during the COVID pandemic, at least until I am vaccinated.
My question, then, is how can I best take stock of what might be a good fit based on my measurements. What are the best tools out there to get a sense of a what a baseline fit might look like? What are the most importance measurement concepts to understand?
I had thought that reach and stack were some good concepts to understand, but I recently communicated with someone who was selling a vintage Olmo frame on ebay. I'd asked them for additional frame geometry details. They only provided the following details in their ad:
51cm (c-c) Olmo San Remoframe-set (52.5cm top tube) c. 80's Columbus SL lugged construction. Professionally refinished with period-correct decals. Braze-on cable guides, recessed brake caliper attachments, Olmo brand engravings, forged front and rear drop-outs. 27.2mm seat post
This didn't feel like enough to understand the frame's geometry. Perhaps because I'm new to this I don't know how to read the meaning of the details provided here. The response I got was:
Seat and top tube lengths are primary frame dimensions affecting fit. Italian stage racing frames of this period are quite similar. I generally recommend people get a frame somewhat larger than if they were a competitive cyclist so the bar and seat heights can be equal or even with bars a bit higher. Racing fit makes no sense for recreational riders.
This makes sense to me, except that I don't know how to understand the frame's geometry and potential fit from just the length of the top tube and the seat post. I'm guessing what they are saying is that that should give me a sense of how much of a racing frame this is? I.e. how much of a bent over and aerodynamic position I'd be in if I were dropped-down?
So combing my general questions above with this particular example, I'm wondering how I could apply some general principles to understand what this seller is saying and also how this frame might fit? Can anyone help educated a newbie? The forum won't let me post a link to the fame on ebay, but it's item id is #114611780974.