Some notes to help:
215 means 215mm width, and since 2.54cm = 1 inch this means it's about (rounding off) means an 8.5" wide tire. Still though it would work a little more is recommended.
The 50 in your #'s means the height of the sidewall is 50% of the width, so ~ 107.5mm height. You can vary the width and height as a %age if you match up the actual result and don't go too crazy. For example a 225 / 45 / 17 tire would be 101.25mm height. Shorter, but not drastic. 235 / 45 / 17 is even better at 105.75mm height.
I think you can do 235 / 45 / 17 at that offset but it's been a while so I'd read backwards and check for people who have run it or go re-read the first post in this thread to be sure.
Thanks for clearing this up. Must have mis-typed in the calculator when I was figuring out what width wheels a 215 would fit.