Originally Posted by
Sy Reene
The tire bead that goes into the rim should have the same circumference whether it's a 23mm or 32mm wide tire. Once the first tire bead is in that center gulley, the 2nd bead has to get over the opposing rim's edge. For a wider rim, that means having to 'stretch' further than it would have to stretch if it was a narrower rim.
Of course the tire beads have a "similar" circumference
The more narrow the rim, the less width in that gully, so less room for both tire beads
I've never seen a road rim so wide that mounting by hand was not possible, on the other hand, mounting a 28mm tire on some old school wheels, can be a challenge, not that anyone would ever do that..