ferrarimanf355 is right that Split/Second has the worst rubberband AI ever known by man.
Which is kind of funny because NFS is the exact opposite. The AI is rubberband neck and neck with me in the racer track and then suddenly it flashes "1 mile remaining" and EVERY CAR slows down to half speed suddenly and I fly by them all and take first by a mile

I don't really get rubberbanding at all. Make your racer with no rubberband and multiple difficulty levels and let the player choose the challenge. If the player is amazing, let them lap all the AI, it's their reward for being that good. If they suck, let them turn down the difficulty until they can catch up.