Open all tracks,
pause the race, select option, then choose sound and highlight FX volume and simultaneously press L1 and L2. Quit the race and when you return to the track select screen you can choose any track. Race on backward tracks, At the track select screen, before you choose a track, simultaneously press L2,R2,X,and down. If you entered the code correctly, an arrow will appear on screen. You will now race on any track you select.
Tips/Hints
Bumper Cars are bad
In single player mode, avoiding bumping other cars (As fun as it maybe) unless you can bump them off the track since it'll slow you down.
So thats how they do it...
An easy way to get ahead of your computer opponents is cutting corners...