In most cases you can get a pretty good swag simply by measuring the rim's inside diameter.
I'll stay out of the tubular - clincher debate, since I am still trying to decide how to rebuild the original wheelset on Capo #2. I rode tubulars quite frequently during the 1970s, but quickly gave them up after moving to north coastal San Diego County with its myriad goathead thorns.
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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