Extra cars:
Start a new race. Choose the "Begin Career" selection. Enter GO_BEARS! (for stock cars) or GO_BRUINS! (for formula one cars) at the "Register" screen. Note: "_" indicates a space.

Wire frame mode:
Enter WYRED at the "Register" screen.

Wide cars:
Enter PHATCARS at the "Register" screen.

Press Start car:
Enter PRESSSTART at the "Register" screen.

In-race car modifications:
Pause the game during a race. Highlight the "Race Statistics" selection and hold R + C. A car editor menu with various options will appear.