I have catered to the bicycle buying public for many many moons, since 1972, and from my position of profound wisdom and experience (?cough!) make the following comments:
- folks used to ride bigger bikes, proportionally, than now. Buyers used to ride bikes that would be considered too big nowadays. This really goes back quite a few years and is supported by looking at ads for bikes even in the 1950s. Many companies had a 21" or 22" as their smallest size offered, and people were smaller on average then!
- You can look at ads and photos from those days and see only a inch or so of seat post "showing." Even many racers rode bikes that were very large relative to their leg length.
- Bicycles imported to the USA were larger overall because there was the (accurate) perception that we beef & corn feed north americans are on average taller than most of the rest of the world. A 23" (59 CM + - ) was considered the average size a 24" was a size likely to be chosen by the 6" tall USA guy.
- In contrast to the assumed average size bike of the 1970s (23"), nowadays the average road frame is a full inch smaller at something closer to a 56 CM for the same 6' size guy.
- The other consideration is the gradual change from to-top sizing to a center-to-center measuring method. Those 24" frames are center-to-top, every one. That = 58.5 CM or so in modern parlance...
- The current road cycling community is much more absorbed in Fit issues than ever before. Our affluent and techno bike world had allowed much more research, study and refinement in bike sizing. I recall being astounded that the Hetchins catalog from the sixties, while talking about all the Bespoke frames, shows less than than an inch total variance available in the top tube length options. Surely some focused riders in those days agonized over fit details & dimensions, but the huge majority were more likely to "get on the bike and ride!"
- Grant Peterson's recent "fit" philosophy seems to result in a lot larger bike than is currently proscribed, more like bikes of yesteryear....
Dale Brown