Originally Posted by
jsdavis
Is that the inner or outer width of the rim?
Inner. Where the rubber meets the rim. Mine are actually 19.5MM from the closest point, but are considered 20's.
Measuring outer doesn't mean too much since rim flange thickness etc. can vary noticeably.
I'd have no problem going as small as a 25MM tire.
For "grins" I mounted a 23MM tire on one of my back up wheels. The rim is VERY SLIGHTLY wider than the tire. Don't think I'd recommend that combination!