Originally Posted by alan_in_tempe

Another way to look at it is that a locked up tire looses grip in all directions, and can no longer track; it can slide sideways as easy as it can slide forwards. Non-slipping rear tires keep the rear tracking, following the front tires.

If the non-slipping rear (or front) tires are leading, then the slipping front (or rear) tires are not so likely to follow the rear. Any side slipping of the trailing tires will yaw the car, steering the leading/tracking tires in the opposite direction which increases the yawing, which leads to a very rapid 180 spin until the tracking tires are then allowed to follow. Even if the rapid spin causes the previously tracking tires to begin to slip, there is a good chance they will regain traction as the yaw realigns those tires back to the direction of forward motion (although those tires will then be turning in the opposite direction as the car will have spun half way around).

It takes extremely good reflexes to control a car with a rear end lock up, requiring almost violent steering inputs.

-- Alan