Unlock a free G-Ride ATV if you have previous save data from Offroad ATV 2 (on the same memory card as the ATV3 Save).
Get Everything
Go into player profile. Then into enter !SLACKER!. This will unlock everything.
All rider gear
Select "Options" at the main menu, then choose "Player Profile". Select the "Cheats" option, then enter FITS as a case-sensitive code.
Ground stunts
Wheelie: Press Analog-stick Down while holding Gas.
Endo: While driving, hold Analog-stick Up and press Brake.
Bicycle: While driving, press Analog-stick Left or Analog-stick Right and R2.