I think Schwinn considered that a 20" frame, but I would report 19" C-C / 19.5" C-T, which is more useful to someone evaluating it for size. The seat tubes of my Capos are 56cm long from the center of the crank spindle, but that includes about a cm of clamp rise, so I go with 55cm C-T, referenced to the top of the top tube.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069