Good luck fixing a chain in anything colder than -10c. Metal has a way of contracting in cold, fingers have a way of freezing when touching metal. Even flats are so tough that when it happened to me once, I rode it out (it was on snow) and fixed it when I got to the office. Best thing you can bring on a winter commute? A pair of runners so at the very least you have comfortable footwear while you run along side the bike.