enever you want to, as long as you have already filled the turbo bar.
Another important thing to consider during the race are the portals, which allow you to take improvised shortcuts at any point in the game. However, you have to pass through them at exactly the right moment in order to take advantage of them.
Retro Future Racing is a very interesting racing game. Though it doesn't offer much variety, it does have different mechanics that are a far cry from those of more conventional car games.