Hey everyone...I've been checking out the forum for about a week now...and this is by far the most informative and helpful bike community I have discovered thus far . I've noticed a few threads inquiring into the same issues as I might be mentioning...but, I hope my question is unique. I have two bikes that myself and my g/f use for commuting currently (both currently have mtb tread tires), and I was hoping to swap the current mountain bike tread tires for a tire of less tread, or treadless (slicks) tires. I measured my rim width (sheldon brown website) for the mountain bike, and it appeared to be 1 inch (25.4 mm) wide. The hybrid bike's rim width appeared to be between 0.93 (23.8 mm) of an inch and 1 (25.4 mm) inch. I was hoping to get some feedback as to the accuracy of my measurements, ie...do these numbers seem right...when comparing to other mountain bike and hybrid bike rims widths you either own, or have seen? Based upon Sheldon Brown's figures, it seems that the narrowest width tire I can fit SAFELY on the MTB is 1.73 inches; about 1.50 inches on the hybrid bike rim. Again...does this seem accurate based upon your own experiences of fitting tires of these sizes to your rims of possible comparable sizes? I apologize for the length of the message...I'm hoping to purchase the tires online today - the reason for my thoroughness. Thank you everyone!