My only experience was with the 26" rims. But I completely agree -I was curious since I had a spare set of Rhynolites if I could use them (plus they are very strong rims) and couldn't find anywhere that could confirm the minimum width tyre that could be mounted. Annoying really..... The closest thing I could find was the Sheldon Brown web site with some approximate guidelines. Another thing is the ability of the rim to handle the pressure (e.g. upwards to 100psi) on the rim sidewalls -course, no specs were available on any manufacturers web site about this. In the end I already had a like new set of Sun CR-18 32h rims, so I just bought a 36h rear rim and laced it up to a 36h hub I bought and used the front 32h I already had -I went on the fact that Sun listed these rims suitable for touring on their website so assumed they would be ok. I can run 1.5" (which I've used for touring) or 1.25" width tyres for commuting now.