The car in this photo (hi-res version) is "doing a wheelie." Note the big racing slicks on the rear wheels--the force of friction that the road exerts on the rear tires creates a torque that rotates the front end of the car upwards. The same effect limits the effectiveness of the rear brakes; in this case the torque rotates the rear of the bicycle upward and reduces the rear tire's contact with the road (see How Things Work: Front and Rear Bicycle Brakes by Lou Bloomfield).
