dddd

FWIW, I ran 23mm Michelins (which seemed generously-sized to my eye) on a pair of 25mm-wide Mavic Module-4 rims back in the late 1990's.

I did all of my hill-loop training on that setup for about two years up in the Santa Cruz Mtns. Never had any problem, and the 25mm-wide rims appeared to protrude just a hair beyond the inflated width of the tires. Cornering felt extremely firm and precise at what I remember being about 95psi for my almost 190lb bike+rider weight.

I built those wheels myself onto a pair of 40h solid-high-flange tandem hubs that I narrowed to 128mm, and with all those spokes and the wide rims plus the vertical sidewalls, no wonder they felt solid! I still have 'em.

I have also run 20mm tires on Super Champ 58's that were 22mm wide externally and had contemporary bead hooks, again with no problems but at a slightly-higher pressure for sure.

HED's newest alloy rim is fully 25mm wide externally (19mm inside, iir), with no warnings against using 23mm tires. These wider (although only 25mm high) rims are supposed to be much more immune to frontal drag caused by crosswinds.

In the pioneering spirit, and at the opposite extreme, I raced MTB for years on 45mm tires mounted to rims only 20.5mm wide! Again, no problems, and at around 45psi.