Join Date: Jul 2000
Bikes: 1959 Capo; 1980 Peugeot PKN-10; 1981 Bianchi; 1988 Schwinn KOM-10;
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My 1960 Gran Sport (second generation???) is rated for 14-26 teeth. I am rebuilding the bike as a 12-speed: 49-46 / 14-16-18-21-24-26, using an ultra-6 freewheel for my 120mm rear axle.
If you have cottered cranks with the 3-piece 3-to-6-bolt Simplex adaptor, you can go down to 45 teeth, and probably 44, in which case you run 47-44, reusing your inner chainring as your new outer. 6-bolt 157mm BCD chainrings are not plentiful, but there is a 52-45 set currently on eBay. With your relatively large proposed jumps on the freewheel (I had a 1971 SunTour 5-speed with 14-18-22-27-34 teeth), you may want to try 50-45 / 14-18-22-26, which should work fine with the Gran Sport.
I have always liked half-step / 1.5-step setups, in which I need change only the inner chaining to accommodate either hills or flats. In the 1970s I used 50-47 / 14-16-18-20-23 or 50-42 / 14-16-18-20-23, depending on whether my route included some serious climbing.
"Early to bed, early to rise. Work like hell, and advertise." -- George Stahlman
Capo [dschaw'-poe]: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger, S/N 42624
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1981 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069