2.5 x 18 ??? When they came with the old dims the more common was 3.00 x21. Cz's came with 2.75 Barum fronts, suposedly better for mud. You can get it in, i use the dry method for an oversized tube, lots of talcum powder or similar for getting it in, just a little bit of air will make it slip in a little bit better. Again though, that tire was intended for the 125/250 f's. like my crf 250 those come with a 1.85x19 rim. So when you wear that one out you have an idea what to shop for.
Got to love it when they "edit" your requests. The strangest one I had was from a dealer called Midwest Action Cycle. I ordered a smaller rear sprocket than stock. They sent me a stock one and when I called them, this very girlie sounding guy said "we shipped you the "right size", you had ordered the "wrong size". LOL thanks for straigtening me out here, old "anything but straight".