To open all of the tracks and stunt mode, at the title screen go to options and 
put the skill level on ameture and the trophy presenter to male. Hit start to go 
back to the title screen and press up, right, down, left, up, right, down, left. 
Then go back to options and put the skill level on professional and the trophy 
presenter to riders choice, then hit start to go back to the starting screen and 
press up, left, down, right, up, left, down, right you should hear a sound, if 
you don't hear it you have to do the code all over.

COOL SECRETS: 
You'll gain access to these cheats only after you unlocked all tracks by 
winning a Full Season at Professional level. Once you accomplish this, a 
bubble will appear on the title screen that says "Codes Enabled". Now each 
time you beat the game with a different team, you will be given a code by 
that team. Each team has 2 codes, and there is a final code presented by the 
crew from Singletrac themselves:

Super Agility: Down,O,Left,L1,Left,Right,Left,Right. (this lets you 
pull tricks quick and easy) 

Zero Resistance: S,L1,T,Right,L1,Down,R2,T. (easier to knock you off road) 

Double Stunt Points: Right,Up,O,L2,Triangle,O,R1,R2. (the name says it all) 

Show off camera enabled: T,Down,S,T,L1,L1,R1,R1. (this really sucks,try it) 

Air Brakes: R1,R2,Right,L2,Up,O,Up,O. (very handy avoiding air wrecks) 

Rocket Racer: T,Up,Up,L2,L2,Up,Up,Up. (makes you run turbo speed all the time,
you'll be winning cypruss track by 30 seconds with the right racer, it rocks!!!) 

Unlimited Turbos: T,O,Right,R2,Up,S,Up,T. (not much use but for acceleration 
with rocket code) 

Ice Racing: Up,R2,R1,Right,L1,Square,Right,Right. (makes everything slippery 
as ice,very hard) 

Two-Player Mode with Other Bikes: O,S,R2,O,T,L2,Right,Up. You and a friend 
can now complete against the rest of the pack, for a total of 20 bikes in the race!

Go to the options screen and set it to professional and 6 laps, then press start. 
At the title screen and press, circle, circle, circle, triangle, triangle, square, 
triangle. A balloon will say "cheats enabled". Then enter your codes. {after 
you put in the codes you can change the difficulty to what you want}