Quote from Scawen :

AI driver improvements

Just recently we discovered that the AI were driving around too slowly because they were underestimating the available grip. But because available grip depends on tyre load in a non-linear way, it turns out that some of the programming for the AI drivers needs a little reorganising. Many community members like to drive with AI in single player mode, so it is important for them to drive at a good speed.

I must say what i think about AI:

Ofcourse if you are pro then AI is too slow, but it's not biggest problem with AI. My opinion is that AI drivers are too general, they almost never make mistakes and so they never get to overtake another AI. Also when player tries to overtake them they usually don't change their lines at all, they drive like you are not there so too many times they end up hitting you.