I noticed recently that serious bike racers(like that of moto gp) tilt their whole body and bike while taking curves. I know that they do so to produce necessary centripetal force. But I wonder how can they tilt their bikes? The biker will exert certain force on bike to tilt it. By Newton's third law, the bike will exert same reaction force on biker. So, net force on system of biker and bike is 0. Then, how is the biker able to tilt bike?