I didn't understand it at first. But it's actually really simple. Corners have amount of times you have to stop in them, which basically means you have to end your turn in that turn 1 or 2 times (or more) depending on that corner. So if its a 2 corner try to have your first turn end in the first half of the corner so that you have enough space next time to gear down and end your turn again in the same corner. Sometimes you come in too hot and need to gear down more than just 1 gear, if you do this it will waste gas, or gas ad breaks, or gas, breaks AND engine. If you over roll a bit you can use breaks to reduce your roll by 1 or you can take it through the corner keep your roll and use up your tires.