On Sears Point Raceway, go for seven turns (or eight if you count the little tiny dip in the track as the fourth turn). Stop after the area of sand at the end of the seventh turn. You will be able to get into the space between the tire barrier and the fence there. Drive along that place for a short while until the fence ends. You should now be able to drive around on the dirt outside of the racetrack with no boundaries (except the edge of the ground).