At the start of the race there is a lodge on the left with a ramp going up. At the top there is another boost that helps you get in the lead.
When the road splits into two, take the left route. After this take the boost and follow the left wall, in a little while there will be another boost which helps you get in the lead.
To access the bonus modes you must meet the following criteria:
Mode B: Get a Bronze Medal or better on every track of mode C.
Mode A: Get a Bronze Medal or better on every track of mode B.
Mode AA: Get a Bronze Medal or better on every track of mode A.
Save your game before you do this trick. Race a friend and make sure you each have a memory card. If your friend wins he will take one of your parts. Have him save his game on his memory card and you load your game from yours, or vice versa if you win.
When the computer is choosing what parts to take, press the A button rapidly. This will make the computer select faster. The good part about this code is that if the computer is choosing from you, you have a better chance of them taking nothing.
Ever wonder how you could get a CPU winner to trade you something for something when he takes a part away from you? Well, go to the title page and press start when you turn on your system and select "OPTIONS". Move your control stick until "PARTS OPTIONS" is highlighted and press the A button twice. Leave "STEAL PARTS" on and turn "TRADE PARTS/SWAP PARTS" on. Now, the CPUs will steal one of your parts (and sometimes none) and no matter what will give you something of his.
Right before starting the race, press the gas button when the last light is about to turn green. If you are playing one player mode and seem to have a hard time starting off, rev the engine until it gets close to 5. Once it starts you off, you should get a faster start.