BOBP

tire dias need to remain approximately the same and one should go one size narrower(205 vs. 225) where is the logic on whether to use 16" dia or 17" dia,again maintaining the same rolling circumference? Or look at it this way: 205/55-16,205/50-17..whats the diff if any or just a matter of taste and affordability?

BrianN

than the 17 inch tire of the same overall height due to the taller sidewall. More potholes and obscured road surfaces are usually the norm in the winter months. A narrower tire will cut through the snow more easily to maintain traction. There is more force per unit area exerted with the narrower tire to displace the snow.
I live in Chicagoland where potholes are common and the roads are swiftly cleared. I went with 225-50-HR-16 Pirelli 210A because I still want to maintain maximum dry traction (vs. the 205/55-16) but have the rim protection of the 16 inch rims. I may need to upgrade to 17 inch snow rims next winter should I decide to go with Alcon B type calipers in front. If you are planning a big brake upgrade, going with a 17 inch snow tire rim size is something to consider unless you want to change out calipers on a seasonal basis. But if you do swap out calipers, then you lose the stopping power of the big brakes for several months. I would opt to keep the big brakes on.
A bent rim is cheaper than the alternative! ;-)