Is it possible to race against computer opponents with different AI? Or do all computer opponents have the same AI level?

Uhm, iirc if you swith between OK, QUICK and PRO before adding AIs you can have different level AIs on track.

And if you race computers that are faster you get more credits...not that it matters in S2.

Apparently the AI also learn a circuit. The more it races the better it gets . . . Apparently. Never use the AI myself.

They do learn to a degree, but I have found that they not only learn a few good things and get faster, but they also learn some really bad lines that cost them tons of time. They also insist on lifting off the throttle on some of the faster sections when they really don't need to.

I think that bobvanvliet is correct on setting the levels.

My suggestion is to let each AI hotlap by themselves on a track. They will get some faster then. If they go in a big group, they usually end up wrecking themselves and then they seem to learn bad behaviors.

I do use the AI some for training for a race. Yes, online is better, but that is not always an option. It makes it a bit more interesting to use the AI. Yes, it is still really annoying when they ram you off the track, but it does teach you to use alternate lines .

Some people like to practice with other cars on the track, so there is nothing wrong with that.