Since this issue comes up, nice calculator to help with "will they fit" questions for tires and wheels. Given the calculator results it helps with being able to compare with stock or other currently run tires and wheels combinations. I'm still pondering what will look right and fit right and what I can afford for alloy wheels and new tires for my Hawk GT. I use photo shop to cut and paste a preview when looking at wheels. Right now I'm pondering alloy wheels 15X6 with 3.5" backspace and 15X7 with 3.75" backspace. right now I have 15X5 steel wheels ( probably 3.25" or 3.5"" backspace) and stock hubcaps with 205/75/15 tires. Will likely switch to 225/7015 tires which will require 6 - 7" wide wheels.
15X5 with 3.25" backspace original rim compared to 15X7 with 3.75" back space; tire sizes indicated on comparison chart