Just like Jim explained. The car can "wheelie" just as he describes because of the pinion climbing the ring gear and the added weight transfer to the rear tires. The car does not wheelie because of it rotating about its center of gravity, it wheelies because of the force through the pinion gear.

In order for a car to do a "stoppie" the front tires would have to be able to supply sufficient braking force that the car would actually rotate around its center of gravity and launch the rear end in the air. The tires could never hope to provide that much grip. The center of gravity in ANY car is much too low for that to ever be possible. Now if you mounted an upright telephone pole through the sunroof and placed hundreds of pounds at its tip, then you could make a car fall flat on its face

Motorcycles can easily do stoppies because of the fact that their cg is so high and because the rider can also shift his weight.

 

Thanks for the actual answers, guys, even if my questions were lame. hehe nice to not get flamed and learn something every now and then