Cheats
Enter these codes at the Main Menu.

Circuit Tracks	Down, R, R, R, X, X, X, Z
Drag Tracks	Right, Z, Left, R, Z, L, Y, X
Drift Physics	R Button, Up, Up, Up, Down, Down, Down, L Button
Drift Tracks	Left, Left, Left, Left, Right, X, R, Y
Sprint Tracks	Up, X, X, X, R, Down, Down, Down

Unlockables
To unlock the following complete Underground Mode:

All Accessories
All Body Parts
All Decals
All Paint Colors
All Rims
All Vinyl