From the Main Menu select Options the select the Cheat Code menu. Enter in one

of the following codes:

Code            Result
UNLIMITEDPC     Unlimited power clutch 
JOKERIDERS      All joke riders 
NOBIKES         Invisible bikes
NORIDERS        Invisible riders 
NDFSPD          Unlimited turbo 
LOFENCES        Low fences 
I AM WEAK       Display riders weakness 
EXPLODE         Exploding text  

At the Cheat Code entry screen you can enter:

Code            Result
OTRATTWTGHWG    The Riverbed 
OSSFMOGLFM      The Launching Pad  
WMXPLIBWWA      The Washougal 
NUTSANDBOLTSS   Parts Unlimited 
NEEDNEWEXHAUST  FMF 
SUPPLIESONLINE  Wrenchead.com 
SHOESANDTRICKS  Etnies Freestyle Games 
THROWMEGOGGLES  Scott 
SHOESANDTRICKS  Etnies Freestyle Games

Unlock Riders

Enter the following codes at the Cheat Code entry screen:

4XUSMXDNCHAMP   Johnny O`Marra 
9XBELGIANCHAMP  Roger DeCoster 
BUNGAVEE        Space Overlord  
DTMHBOSS        Bradley G 
ENDZONEDANCE    Smitty Sugarlegs  
FORTYFOUR       Bob Page  
HARVEYSAYSRELAX Hot Tub Harvey 
HONORFIRST      Moto Samurai 
IRONMAN         David Bailey 
JOUSTER         Sir Dirthead 
LETSGOEAGAL     EA Gal 
LOVESBRAINS     The Zombie  
LOOKMANOBODY    Doctor Invizzo 
MARROWMAN       Bones
MASKEDMAN       El Luchador 
MELLOWOUT       Tie Dye Guy  
METALDUDE       MR-34 Robot 
MMMSQUIRREL     Harry Bigfoot  
ONESMALLSTEP    Astro Nut 
PEANUTBUTTER    Agent Albert 
PLAIDROCKS      Brave Scotsman 
POSSUMPANCAKES  Billy Ray MudMullet 
POLKADOT        Tricky The Clown 
PYRAMIDSCHEME   Sarcophagus Jones 
SIDEBURNS       The King 
SQWAK           Marimba  
THREEPIECESUIT  Spitt Polish 
TRIPLELEAPER    Supercross Avenger 
WHOSTHAT        Some Guy 
WWWECKOCOM      Ecko Rider 

Thanks to Revolution reader Bryan#48!