Wheels fall off on Volvo (In Car Talk newspaper column.)

Why did the wheels fall of. I think you missed the physics of fatigue by saying the lug bolts were over tightened. For fatigue to occur there has to be repetitive strain (stretching)in the elastic region of the tensile strength. If the bolt is over torqued there cannot be repetitive strain. Fatigue occurs if the bolt is under torqued so that the wheel can move from the backing plate and cause repetitive changes of stress. Fatigue will be a flat break with a curved area where the failure started. Excessive torque failure will be characterized by a necking down in the area of the break.