I had a look at it and its very good, There used to be an Exel spreadsheet that did exactly the same in the downloads section on here but I can't even find the downloads section today to show you
Anyway, I have it copied to my hard drive, one of the handy parameters in it is that you can change the tyre size and aspect ratio so it even tells you your gearing for supermoto wheels.
I would have replied but as I already had something that did pretty much the same thing I didn't.
Regards Scott.