|Quoting Continental (Reply 6):|
How does a wheel just fall off? Did the tire blow first before it fell?
Poor maintenance (I'm a mechanic, so I'm biased to say that this is the less likely possibility) or metal fatigue.
The wheel assembly is held on with a lug nut, which is torqued to a specific value set by the manufacturer.
The lug nut is then held in place with, not one but TWO bolts, inserted THROUGH the threads of the axle. This should keep the lug nut from coming off, even if it worked itself loose from the torque value somehow.
So, needless to say, one coming off is "not possible." Yet, it happens periodically.
The end of the axle has been known to break off, taking the lug nut and safety nuts with it, which would definitely allow the wheel to zing straight off the end.