I actually had a set of wheels, complete with drum come off the passenger side of my front trailer and I can tell you that the usual cause is bearing failure in the hub. I was a freight hauler almost all my career and they all used cast iron spider type hubs, I don’t know how a trailer with Budd wheels hub is made.
I had made a pre trip inspection when I hooked up the set of doubles and was about 50 miles heading East out of Buffalo on the Thruway. There was no warning whatsoever when the reamost set of wheels and brake drum and hub came off, hit the guard rail bounced into the landing gear of the second trailer knocking it loose which sent it down into the median and when it came out it passed right over the Hyundai Excel driving the other way.
The driver of the Hyundai stopped and backed down the shoulder while I was setting up my reflectors. He said something from your wheels broke my windshield . I was skeptical but went over to look. His windshield was all cracked but there was a rectangular hole in it about 3 inches long on the passenger side. When we looked inside , there was one of the wheel bearing rollers burned into the floor mat.
To think the driver would hear or feel something first is a mistake. The amount of vibration and noise inside a freight tractor used to be deafening We all retired with hearing loss and even though it was on the front trailer it was still about 50 ft. behind me and on the other side. Why would it wobble, the drum and both wheels and hub are bolted together and quite stable?
One of the things that led to this failure was the way union freight drivers are paid in Buffalo, and the fact there is a division of labor between city and road drivers. City drivers are hourly paid and do all local work and all driving work at a freight terminal. The road driver does not hook up his tractor and trailer , load it, seal it or fuel it. If he did do any physical work at the terminal, even pulling a dipstick he would have to be paid 1/2 hour or time spent whichever is greater. He is required by law to do a pretrip inspection. In order to not have to pay the road driver , the companies insist that the drivers do the inspection without touching anything. The wheel bearings are oil filled and have a rubber cap you can pull off to see how much oil is in them. The DOT would like us to check them as well as many other things that we would need, creeper, coveralls, gloves and flashlights for. The companies we worked for insisted we were to do none of those things, they were not our trucks and they would fire us if they caught us working on them.
We never did find the set of wheels, they disappeared into a cornfield with a wood behind it and there was a steep embankment to get down to it. I was on the scene about 6 hours, You have to wait not only for the state police and fill out an accident report, but then you have to wait for Thruway inspectors to come out from Albany or Syracuse and fill one out for them, They inspected both trailers and the tractor for long doubles operation because of lack of maintenance and I had to drop one trailer
and the dolly at the next exit. And also, no lock washers involved but my opinion is the the news never gets mechanical things right.