Cheats for Ridge Racer DS (DS)

Reverse track
To play on a reverse track, drive forward at the starting point until you get to fifth gear. Then, make a "U" turn and drive towards the wall. If done correctly, you will hit sixth gear and the wall will disappear. The track will now be in reverse.

Bonus cars
Play ten multi-player races using a single cartridge to unlock the 00-Agent car. Keep playing in multi-player mode to continue unlocking bonus cars, in the following order: Red Shirt Rage, Pooka, Caddy Car, Galaga '88, Shy Guy, and Mario Racing. Win all the Platinum GP races to unlock all bonus cars in the game.