Joined: Nov 2006
Posts: 19,811
Likes: 596
From: NJ, NYC, LI
Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...
My Holdsworth 650b conversion is really tight with 42mm tires (Hetres) on Weinmann ZAC19 rims, especially so since the tires don't seat well.
Really tight, like it varies between 1 and 3 mm over the course of a wheel revolution. Potentially a real problem, but I've ridden it a couple thousand miles without an issue.
Nonetheless, on long rides (i did a fleche and an arrow this year, a 300k last year, &c) I have carried a 38 mm tire (just in case) and obviously I'd have a little less to worry about if I had a little more clearance.