Exercise is not designed to lose weight, it's designed to get you fit. Diet is designed for you to lose weight. You can exercise all you want and without a change in diet, you won't lose weight.

If you want to use biking for weight loss, consider short rides, max of 20 miles, and more often. I find longer rides make me hungry and I eat more. I now can ride easily up to 50 miles without having to eat anymore but then if you are cutting back on food, you may find yourself running out of energy.