The dice used in the Formula D game are unique and cannot really be found anywhere else. Also, when you play the game with four or more players, it can get cumbersome to pass the dice around the table. This can be avoided by purchasing a second set of die, one for each side of the table. It also ensures that if you lose one of your unique die, you're awesome game won't immediately become useless!
Add some convenience to your Formula D game with more dice. Makes it nicer so that there is less cross-grabbing of dice when you find everyone is using the same gear die around a certain section of track.