If you view commuting by bike as primarily a way to exercise and lose weight, you may find that you don't stick with it if you don't see results quickly. By all means try it, but try not to make it a means to an end...make it an enjoyable part of your day, with the added bonus of getting some exercise. If you lose those last 10 pounds (btw...are you trying to make some of us jealous?), then great! But if not, you'll still have made a great decision and hopefully had some fun!