I'm thinking of getting a Model S with 21" Wheels and then buy the Pirelli Winter Wheel and Tire Set from the Tesla Gear store at a later time. I noticed that if you order a Model S with 19" wheels, it will come with 19" Michelin Primacy tires. Anybody know what the differences are between these two tires? If the Michelins offer 3% range increase, is there a way to get those instead of the Pirelli tires from their store? Are the Pirelli tires strictly winter tires and the Michelins are all-season tires?