Joined: Jan 2010
Posts: 9,826
Likes: 1,805
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
I hate to quibble with 2 diameters, but remembered reading somewhere that 2-1/2 diameters was the safe figure! All I can say is I've actually ridden briefly on far less, not that I recommend that, and keeping in mind I weigh all of 155lb.