I just read an article in Popular Science about it. They compared the real cars on a track to the game's virtual car and track. They took a pro driver and street racer RJ Devera and let them both play the game, and then had them drive the real thing. The track was fairly close according to the pro, and the times were reasonably accurate, too. The pro beat the street racer pretty handily on both the real track and Xbox game. To be fair though, it was the pro's home track.