Wheel size setting in custom tune options?

Hi.

I've got an iTSX and a couple of custom performance tunes for my Raptor. They work great and make the truck a helluva lot more fun!

In the spirit of making it even better I've got some new wheels and tires coming soon and they're going to be 1.5-2" bigger than the stockers. When I first got the app I noticed that changing tire size was an option in the interactive demo. The other day I went looking for it on my custom tunes and can't find it. Is there something special I have to do to make this option or available or does it need to be done when the tune is created?

should be a user option tire rev to adjust for tires, ck to see if its off first before adjusting

Thanks. I'll give it a look the next time I switch tunes. (probably next fill up)

Another quick question, does it just have a bunch of preset/common tire sizes to choose from or can we input a specific diameter? The tires I've got coming are 315/70r18's (35.7" actual diameter) so somewhat uncommon. Will I be able to adjust it for these or will I need to just pick the closest match?