Enter the following at the Title Screen...

Pocket Bikes:
Up, Down, R2, L2, Down, Up, L1, X.

Turbo Boost:
Up, Up, Up, Triangle, R1, Triangle, R2, Up, Up, X.

Reverse Mode:
Left, Right, Left, Right, Circle, Circle, R1, L1, Triangle, X.

All tracks:
Up, Up, Left, Right, Down, Down, Circle, R2, Triangle, X

All Reversed Tracks:
Down, Down, Right, Left, Up, Up, Circle, L2, Triangle, X.

Night tracks:
Up, Circle, L1, Down, Triangle, L2, Circle, Left, R1, X

CPU goes slower:
Down, Down, Down, Circle, L1, Circle, L2, Down, Down, X

See the Credits:
Circle, Triangle, L2, Circle, Circle, Triangle, Circle, Up, Right, Left, X

View Victory FMV:
Circle, Triangle, Circle, Triangle, Circle, Triangle, L1, Up, R2, X.