I ran 205/40 17 Blizzak's on the ST and had great luck with them, however, I suggest going with a 15" wheel with a narrow tire. A narrow tire cuts into the snow better, the extra sidewall protects the wheel from pot holes and debris, and the smaller wheel keeps the rim out of the snow so there is less build-up to put the wheel out of balance. Also, chances are very good that the dealer will destroy the stock wheels when they install the snow tires. A few seasons of swapping tires and the wheels are junk. I run 14" snow tires on my 2011 Fiesta and the cost of 4 wheels and tires was much less than 16" snow tires that I could install on an extra set of 16" wheels I had laying around.