The plane which is defined by the head-to-foot and anterior-to-posterior directions in the human body. A stack of images acquired in the sagittal plane separates images by their left-to-right locations. The mid-line sagittal plane bisects the left and right half of the human body.
Under heavy braking, the rear tires lock up and the axle begins to bounce; the amplitude of the bounce becomes so severe that the tires finally develop enough traction (when slamming hard against the pavement) to rip the whole axle assembly free of the vehicle.
If they break entirely, it can cause a wheel/tire combination to fall off the car while at speed, leading to a very unsafe driving situation. Prior to 1997, most cars, trucks and SUV's manufactured and sold in the US had an inner and outer bearing on each wheel that is recommended to be serviced every 30,000 miles.