Fortunately, no one ever came up with true 27" / 630mm tubulars, just as no one ever challenged the metric system for electrical units.
In the U.S., 27" clinchers were ubiquitous through most of the 1970s, but 700C made steady inroads and eventually too over completely by the mid-1980s.
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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