Trucks (and tractors with trailers) throw treads regularly - an entire tire is a bit unusual, and "stuff" does happen. (See part 2, below).
Recaps are standard for the tandem axles and for the trailers.
(Feds require *new* steer tires)
It's possible the driver didn't know he lost the tire - think of the threads on the 5th forum where somebody gets notified by another driver he has a blown tire on his trlr.
Part 2 - the "stuff" that happens.....
Busy 405 freeway in So CA.
Car traveling N/bound loses a wheel and tire which jumps the divider, misses a couple of cars - then hits a S/Bound car in the windshield. Fortunately only minor injuries to the occupants.
We are on-scene for the injuries - can see the N/bound car on the other side of the road about a 1/4 mile away.......but scratching our heads as to where the tire & wheel went..:h
(The car that was hit was in the fast lane)
Then one of the guys points.....*UP* !!
Tire and wheel are lodged in an overhead freeway sign about 300' further down the road!..:W
~