If you check most tire guides (like the Yokohama site) you will find that the 9 inch wheel has three sizes for it. Min (245/xx/17) Ideal (255/xx/17) and Max (265/xx/17). I have been happy with my 255's when I went with Kumho Victor racers or BFG G Force tires. But with the Sumotomo HTRZ II, I found that the 265's are the better fit. It seems that the number is an approximate size and not the real number you get or maybe it is a metric/imperial thing. I just know that tires seem to vary with width depending on maker.