Unlock All Cars Quickly
To unlock a car you must have started a race with it in championship mode. But instead of going through all 22 cars, save the game when the season ends and the next time you load a new season starts. Pick a car to go into race 1 then quit. The car is now unlocked. Keep doing this for every car and then of every season.
Successfully complete championship after unlocking all 22 cars to unlock mirrored tracks.