Binkyboy wrote:"Can anybody with more experience than me on Touring Frames explain why most 531st frames are either 22 inch or 23 inch? Most what I'd call racing frames seemed to go 22 1/2 and 23 1/2 etc. Is it a European influence? From memory all my bikes have been going up on the 1/2 inch as far as I can remember. I currently ride a 22 1/2 inch 531 steel racing bike frame with the stem and saddle level (bad back) I'm 5'10" with a 32" inside leg. The stem and seat post are showing approx a few inches so in theory I could go to a 23 inch. I'd welcome any thoughts on this please."
The frame size is determined by the builder, based on
a) what the customer specifies (and that could be down to the nearest mm if needs be, because they are cut to suit,
b) the most common heights of typical buyers, if he is building for stock. Hence the preponderance of mid size frames.
In the good old days, the frame size (as measured up the length of the seat tube from centre of BB to top of seat lug) was your inside leg length, without shoes, less 10". This allowed for crank length and seat pin and saddle height.
I'm 6ft and, using the above formula, where my inside leg length is 34", the frame size is 24", and that's what all my traditional steel frames have been.
The modern "compact" frames with sloping top tubes, are anyone's guess!
But even with the traditional arrangement you would still be taking pot luck about reach to the bars unless you did more research. With sloping top tubes, reach to the bars is effectively the determining factor. Seat tube length is something you don't have to consider. I find it easier to accurately reproduce my ideal set-up on a semi-compact frame. So long as the published geometry is correct.