Around 1970 I saw a large tire and wheel fall off the back of a truck and roll into traffic. I was on a Troy team bus and all of us watched as it hit a car just about head on.
It really crushed the car. I never did hear what happened to the passengers but it was bad. The coach immediately told the driver to keep going.
Over the years I have seen numerous wheels with tires come off trucks, buses and cars and flying down and across the freeways. One I saw came off a bus, went over the center divider and hit a car head on and bounced over it and kept on going. This was in the Los Angeles area and traffic was not moving but maybe 10-15mph.