The nearest equivalent usually given for 30 x 9.50 x 15's is 235 / 75 / 15. But there is a bit of a difference. Kbkel is spot on. Put a 235/75/15 beside a 30/9.50/15 and you will see the latter is slightly taller and slightly wider. Like Kbkel's pic.-not a huge difference but you would definately notice looking at the two together. I did exactly the same thing with one of each tyre unmounted and 30 / 9.50 / 15 is the best part of an inch taller.