For the moment I have an AI car, that follows points (let's call this Waypoints), that I built by myself.
Of course, it's not optimal because of my poor human hand, and car knowledge.
After this drawing, I put waypoints (about 80) on this red line, and my car is able to follow it (and dodge other cars, but that's another story).
But... It's not perfect: I read some articles, but I don't know how to implement the generation of the perfect path..
http://www.drivingfast.net/techniques/racing-line.htm (speaking about an 'Apex', but I don't know how to find this particular point)
"Searching for the Optimal Racing Line Using Genetic Algorithms" (too complicated for my little game)