All of the cheat codes have to be entered in the Cheats menu.

All Bonuses
TOOLAZY

1,000,000 Points
BROKEASAJOKE

50cc Bikes
MINIMOTO

All Gear
WARDROBE

All Riders
WANNABE

Freestyle Tracks
HUCKIT

All Machines
LEADFOOT

All Tracks
PITPASS.

Unlock Everything
TOOLAZY