I‘m trying to buy some tires to start rebuilding my girlfriends Cruiser we got at a garage sale, and I‘m wondering whether or not I can switch out tires marked 26 x 1.75 with tires marked 26 x 2.125? My girlfriend likes Hello Kitty, and Nirve has some 26 x 2.125 tires with hello kitty on them that I‘d want to get if I could.
The rims should be able to fit the larger tire. But you need to check if you have that extra clearance on the bike frame. Just don't mix fractional sizes with decimal: 26 x 1 3/4 is a different size than 26 x 1.75 In short, you're probably good to go on the change.
The 26 is the diameter and the 1.75 and 2.125 are the widths. Those 26 sizes use compatible rims so you can interchange them. But look at this page to see how complicated things can get.
The tires will fit your 26 inch rims. You will probably be OK, but take a look at the current tires on the bike to make sure you have some additional clearance between the tire and the fork up front and the stays in the back. If you have sufficient clearance for the wider tire, you should be good to go. HTH
