-To turn sharp corners fast, tap B while turning. This also works while using nitrous.
-Before going into a sharp turn in a car with a manual transmission, downshift just before you start your turn. Then, start the turn and hit the Speed Breaker. Just before you reach the direction you want to go, turn quickly in the other direction, turn off Speed Breaker, and turn straight. Hit the nitrous for about one second, then shift up when you need to and you should be on your way.