Crunches/sit-ups routine at proper siet ang nagpapaliit ng bilbil.
Actually, doing this will make your ab muscles grow, pushing out the fat, hence making you look "fatter".
You have to make sure you have low body fat % before investing in more crunches / ab routines, else your fat will be pushed above by your growing muscles. So burn the fat first. And biking is a good way to burn fat