Mine is 55! I guess being a track frame it doesn't follow the usual road frame perspectives. I prefer a 54 road frame but the bianchi rides great, I have a bit more upright position than I would on a smaller size. Since I only ride it on the road I don't need the aggro velodrome position that a ~53/4 would give.
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1989 Schwinn Paramount OS
1980 Mclean/Silk Hope Sport Touring
1983 Bianchi pista
1976 Fuji Feather track
1979 raleigh track
"I've consulted my sources and I'm pretty sure your derailleur does not exist"