Wheelie car on tires Can someone explain for me in detail what causes a car to pull off with a wheelie. I know that there is a lot of g force on the rear wheels when the car launches forward but how does that cause the weight push like a lever on the rear wheel and pivot the front of the car up. I am having a hard time visualizing intuitively where the down force on the rear of the car comes from. Also does the fact that usually the front tires are much thinner than the rear tires contribute to this in any way. 
 A: A slightly different analysis may make the situation clearer:
You are looking at the rear wheels of a car that is about to launch from right to left.  The engine, through the drive train, is exerting a large counter clockwise torque on the rear wheels.  That torque is resisted by the friction between the tires and the road surface.  It is this friction force that drives the car forward.
However...
The CCW torque exerted by the rear axles on the tires creates an opposite, clockwise torque from the tires on the car;  the tires are trying to rotate the car in a clockwise direction, lifting the front end of the car as it rotates around the rear axles.  The force of gravity on the mass at the front of the car, on the other hand, is exerting a CCW torque, keeping the car from rotating.  That's why some drag cars classes are so long from the front wheels to the rear wheels.  The length of the car maximizes the CCW torque from the mass concentrated at the extreme front end of the car.
Consider a related system.  The engine of a helicopter exerts a torque on the blades, to overcome the drag torque from air friction on the rotating blades.  But this means that the air is exerting the reverse torque, through the engine on the frame of the helicopter.  The blades at the rear of the helicopter, with a horizontal shaft, exert a balancing torque to keep the main blades from spinning the helicopter.
