Cheat:

In National, head off the course, straight as possible. 

When you come up to the wall make sure you are going at least 70 Mph. and go straight up the wall. 

This is the only way you can get up to 100 Mph. 

If you continue forward when on the cliff, there will be an explosion sound and you will go about 100 feet in the air.

When at main menu of game type "kcussedocruoy".

Enter your name as "HONDAISACE".

In the stunt quarries, follow the AI motorbikes to find a good circuit with plenty of jumps; then just repeat that circuit over and over, pulling the same stunts to score points.

 

Leaning back and forward can be just as important as steering, especially when you're landing or going up slopes.

 

To avoid flipping over the handlebars, try to land on your rear wheel first.

 

To go forward, don't shove the joystick all the way into the forward position. Keep the joystick's forward/back position nearly centered. If you shove it all the way forward, the rider's weight will shift over the handlebars, making the back end very light and loose. Likewise, pulling back on the joystick makes the front end light, and you'll tend to pop wheelies or lose steering control.

When you jump, press the PRINT SCREEN key several times to get lots of points.

When you are playing tag or are in practice mode and you fall, press the TAB key and you will get right back up.

Enter the Baja race, go towards the outer walls. 

While gaining speed, lean back and keep going towards the wall. 

If you can get to the top go away from the cliff. 

You will be shot into the air like a cannonball. 

You will sound like one too.

When you hit a ramp press [print screen] a couple times, when you land you will get a huge amount of points. 

*Note: This code only works in the retail version