I remember reading an article once on exercise and how people stop biking, jogging, walking (for exercise) in the winter. The author went on to say that people who do that are just looking for excuses to not exercise b/c if you were going to send them on a skiing trip, they would go. If you can ski in the cold, you can bike in the cold. You just have to make sure you are dressed appropriately, just as people do when they go skiing.