Cheats menu
Press L, C-Up, C-Up, C-Down, C-Up, C-Down at the main menu.

Tricks
Hold the R button for the following tricks:

Nac Nac = Z
No hands no feet = Down Z
No hands = Right/Left Z
Side prone = Up Z
Can Can = A
Recliner = Down A
Cliffhanger = Right/Left A
Scorpion = UP A
One foot Can Can = B
Surfer = Down B
Super Mac = Right/Left B
Rodeo = C-Down
Suran wrap = Down C-Down
Toe clip = Up C-Down
Fender grab = C-Left
Backflip = Up C-Left

5 Gear bicyle
Press A, B, A, B, A, B when the race is about to start and when it does, your bike will turn into a 5 gear bicycle.