No roof flaps:
Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. In the game folder, open the folder with your player name. Use a text editor to edit the file "player.ini". The first number you see should be "1". Change it to "0". When you play the game and go backwards at a fast enough speed, you will fly into the air and possibly do some flips.

Drive off track:
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).