Originally Posted by
nfmisso
The important numbers are:
RIM Markings: 622X17
Tire Markings: 42-622
Everything else is marketing gobble gook.
You are correct. The "42-622" is the ISO markings and is most likely the "real" width of the tire, i.e. the tire is 42mm wide. I'm not sure why some manufacturers make tires wider than they are marketing them but there are a number that do. Some are even much wider than the "advertised" width. I have some Vittorias that are supposed to be 32mm but they are marked 37-622 and they are very wide.
Originally Posted by
nfmisso
I would not put anything wider than your current tires on those rims.
As noted by Andrew; as narrow as 25mm would work.
You are being much too conservative with your tire widths. I regularly run 55mm mountain bike tires on 17mm rims without issue. Granted they aren't high pressure tires but I can run them as high as 80psi without problems. I could probably go higher but I run out of nerve before then.
As for how narrow a tire you can put on that rim, a 23 would work just fine. The Velocity A23 is 18mm wide and is
designed for use with a 23mm tire.