The number is what gear a computer driver in your car would be in for the next turn. You are not a computer driver. For a long time at the beginning of the game, my rule of thumb was that number minus one. I'm at 30% and I have most all of the tracks memorized so I know the gear. And if the number flashes, the computer driver has already started braking, meaning you're going too fast. But it won't start flashing unless it's there, which can get you into trouble in a really fast car. My Camaro race car, for example, 950 hp, hit a couple walls in Tokyo because I was waiting for the number. Use it until you memorize the tracks.