Originally Posted by
urbanknight
Back in the steel frame traditional geometry era, I was fairly good at guessing size by sight. Compact geometry and wildly varied tubing thickness gives me no clue.
This is very true. Once you get to oversize tubing, sloping top tubes, and dropped seat stays, guestimating size becomes much more difficult. But mostly I've been in the market for traditional steel frames. For example, last year I was looking for a Centurion Ironman in 57 cm, and a lot of the listings in Craigs List or FB Marketplace just say things like "Medium" or "Large", or the seller doesn't know how to measure, or doesn't say whether they measured C-T or C-C, and some measure the top tube instead of the seat tube. I got pretty good at spotting 58s based on the length of the head tube and where the pump peg was on the head tube in relation to the down tube.