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Thank you @clubman, do you mind me asking how tall you are? I'm guessing you're talking ctt as your measurements are in inches.
I'm 5'8" and my modern bike is a 54cm ctc and that seems about right. I did have a bike fit a few years ago and if I remember, they thought it was ok, certainly can't remember being told it was too big/small. [The main take away point I can remember is that the 172.5mm cranks the bike came with were at the top end of what they'd recommend and I now have 170mm on pretty much all my bikes.]
That bike is square (horizontal top tube naturally) but feel I could have a longer top tube / stem projection than the averageish I've got (I think from memory 9cm give or take a cm). Also think I have about two fists of seatpost showing, although we are not together at the moment sob. Long story short, I think it gives some scope to have a slightly bigger frame with less seatpost.
The ctt measurements give a bit of variability, for example the lugless Hobbs frames have nearly an inch of seattube above the toptube for the clamp. I think the one I have is 23" ctt but the ctc I measured was 56cm.
veloham-
I was 5'10", but I've probably shrunk a bit - this is caused by compression of the spinal discs, but I guess my legs are the same as ever.
Yes, I measure frames from the centre of the BB to the top of the seat tube, but in the case of a lugless frame with a projection above the seat tube for the clamp, I would measure to the level of the top of the top tube. It's worth remembering that virtually all old British built frames will have been built to a round number of inches or half inches - it would be rare to find one that was say, 22 and three quarter inches, for example.
Bike fitting does depend on the opinion of the person doing the fitting. I had one done before deciding on the last frame I had built, but the result was a bit disappointing. The 'expert' had decided that I was a fast pedaller and recommended a 75 degree seat tube - I never did a decent ride on that frame. Of course it might have been due to my own failing powers.
In the end you just have to find what is most comfortable (of efficient ) for you at whatever purpose you're using the bike. Alternatively if you want to look in period you may well have to put up with some discomfort and inefficiency.
clubman
Frame Size Fashions
I agree with Absurdbird that in the fifties the fashion was for largish frames with only a small amount of seatpost exposed.
It's in the nature of fashion to react- mini skirts will inevitably be followed by maxi dresses, at least for a while. Cyclists like to think, when they are specifying their new kit, that they are making decisions in accordance with recently discovered engineering principles. They hope these new ideas will help them go faster than the previous generation of riders and, naturally, the trade is not going to discourage ideas that involve their customers buying new equipment.
In the Edwardian period (pre WW1) it seems to have been normal to have the saddle pretty much directly on top of the seat lug - this may well have encouraged the sloping down top tube which was common at that time. After the war the opposite style became the norm with plenty of seat post exposed, and this is probably why many of the surviving inter-war frames are on the small side. Naturally, post WW2 , as Absurdbird says, the fashion went the other way and there was less seatpost on show. Not everyone followed this trend and it's important to remember that money was scarce: many of us made do with what we happened to have.
When I ordered my first frame as an adult puchaser in 1975 I thought I needed a 22.5" frame, and possibly I did, because it was hard then to find a long seat pin. Gradually I've reduced my desired frame size to 21", and I feel much happier with this - too big a frame makes it hard to ride out of the saddle as the top tube gets in the way.
It seems to me that the limitation on reducing frame size is the amount of the handlebar stem above the headset that you are prepared to tolerate, so a headlclip h/set gives you another inch to play with.
So, right now I'm going out fot a little ride before it starts snowing - my machine: 21" Sunbeam, with headclip.