Originally Posted by
Leisesturm
And I have no idea what would happen if someone mounted a 1" tire on a 25mm wide rim but I for one wouldn't worry about it.
I do. You would wind up denting the edge of the rim and increase potential for blowout because the tire is not wide enough to cover the rim edge. Sheldon Brown has/had a page on acceptable rim/tire widths, which I recall consulting 10+ years ago after I ruined a Sun Rhyno-lite 25mm rim by using it with a 1 tire for commuting.