All tracks - Earn gold medals in every event. 

18 best laps - Enter the name .lapt18 at the start of the game

All 9 driving test finished - Enter the name .test9 at the start of the game

All six meets won - Enter the name .meet6 at the start of the game

GP Mode finished - Enter the name .prix at the start of the game

Set respect points - Enter the name .resp(insert number) at the start of the game to start with that number of repect points. For example, .resp 42 sets the respect points to 42
Sent in by Jenny & Mark

Master code:  Enter borkbork as a name. This code also unlocks the Secret Nevada meet, the Casino Run course, and six more leathers, all GP modes, all bikes, all lids, and lap times.

Respect points:  Start a new game and enter .resp followed by a space and a number (for example, .resp 30) as a name to begin with the indicated amount of respect. Note: Enter .resp54 to unlock all six respect bikes.

Finish all nine driving tests with gold:  Start a new game and enter .test9 as a name.

New meets, street racer bikes, and more courses:  Start a new game and enter .meet4 as a name. You will unlock the New England, Detroit, London, and the Swiss Alps meets; five street racer bikes; and sixteen additional single race, time attack, trick attack, and head to head mode courses.

Additional mirrored GP modes:  Enter .prix3 to unlock three more mirrored modes in the Grand Prix.

Grand Prix mode:  Beat the top record in time attack mode.

Quick start:  Hold Gas + Skid, then release Skid after the countdown.

Tricks:

Wheelie: Hold the Left Analog-stick Back.
Standing Wheelie: Press Trick + Left Analog-stick Back.
Surfing Wheelie: Press Trick + Kick/Punch + Left Analog-stick Back.
Cross Surfing Wheelie: Press Trick + Left Analog-stick Back + Front Brake + Kick/Punch.
Endo: Press Left Analog-stick Forward + Front Brake.
Surfing Powerdown: Press Trick + Left Analog-stick Forward + Power Down.
Handstand Powerdown: Press Trick + Skid + Left Analog-stick Forward + Power Down.
Surfing: Press Trick + Left Analog-stick Forward, then Left Analog-stick Back.
Handstand: Press Trick + Left Analog-stick Forward, then Kick/Punch
Pavement Ride: Trick + Left Analog-stick Forward, then Skid.
Donut: Hold Brake + Gas and turn in one direction with the Left Analog-stick.

Back and frontflip:  Get a powerdown and boost it about 350 feet before a ramp. When you are in mid-air, hold Up or Down to perform a backflip or a frontflip. Note: You need a lot of speed and a very fast bike.

Dodge cars while turning:  While turning, press R. Wait until you are in front of a car and point the Left Analog-stick the opposite way that you are turning. You will keep turning, but at a slower rate. Note: Do not release R until you dodge the car(s).