You can change the tire sizes a little bit... you definitely can if increasing rim diameter, it's called plus/minus sizing. I have a Subaru with all seasons (Continental DWS) and dedicated snow tires (Bridgestone Blizzaks). I run a narrower snow tire since it helps plow through snow a little better. I'm not sure how to get the numbers, but you want to stay under 3%. Somebody else will know what they're talking about much more than me.