If you’d like to make a little money on the side, several civilians throughout the island are hosting a series of racing challenges. These are activated by clearing out various outposts in the same general area, and take the form of a wager between you and the race director. If you can complete a one-way course through the island before time runs out, you win.
You can run a challenge course for free as many times as you want, or put down $50, $100, or $200 as a wager towards your success. Victory earns you that much, while defeat means you lose your money.
Unlike Supply Drops, success in a racing challenge is tracked by hitting markers on the course rather than simply reaching the finish line. As such, you cannot skip any of the markers and still complete the race.
Racing challenges are strictly for fun and provide an entertaining diversion from the life-or-death nature of most of the other side missions in Far Cry 3. Your success, failure, or complete avoidance of these minigames does not affect your completion rate, does not unlock any bonuses, and has no associated Achievements or Trophies.