Centre to centre about 58.4 cm assuming 531 has a diameter of one inch and the 73 degree angle of the frame doesn't make that much difference.
Where are you that measures 30 odd year old frames centre to centre?
Shaun
Canada- in North America- we give both all c to c and center to top- the top of the top tube on vintage bikes can be curved etc which can through off measurements
@midlife started
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Centre to centre about 58.4 cm assuming 531 has a diameter of one inch and the 73 degree angle of the frame doesn't make that much difference.
Where are you that measures 30 odd year old frames centre to centre?
Shaun