Type in go bears! exactly like this and you will receive the top racing teams cars. Another code is go bruins! these codes are for the stock cars and the indy racing cars.
Bonus Cars
Start a new race and select the "Begin Career" option. At the "Register" screen, enter "Go Bears!" for Stock cars, or "Go Bruins!" for Formula One Cars.
Change Car Color
While racing, pause the game and go to the Race Strategy screen. From here, press and hold L1 + L2 + R1 + R2 + X + Circle + Select.
Master Options
While racing, pause the game and go to Race Standings. Now press Circle + X (you might have to do it once or twice.) An option screen will appear which allows you to change the speed of your opponent, gas mileage, tire wear, and more!