When reaching a sharp turn that requires you to use a SpeedBreaker, make sure that before you use it that you have already started a slight turn. When you get into SpeedBreaker status, turn hard, but not so hard that you fishtail. It should be more like a half push on the Analog-stick. Leave it there for a split second. Once you start turning sharply, do not do anything else except keep pressure on the throttle. If you fishtail, turn until your wheels are going the direction you want to travel to come out of the SpeedBreaker with good speed. Make sure the camera is behind the car instead of looking at its side. Then, release the SpeedBreaker and use the nitrous (if available).