Simple achievement providing you can find a game.
From the main menu select xbox live, play. Change the game mode to championship, everything else can be left as not important. Once you find a game you just need to complete 4 races, position isn't important.
Be aware that despite only spending about 20-25 minutes actually riding, this achievement will take the best part of an hour (if not more than) to complete due to the ridiculous loading times.