Train tires

Trains have tires. I didn’t know that. I’m not talking about subways or monorails but actual freight trains. The ones that we have to stop traffic for. They have a steel tire that is heated and expanded until it fits over the steel (or iron) wheel. When the tire wears, it can be turned on a lathe or replaced.
They started doing this because replacing the whole wheel was expensive but it also took more time. There were many different types of wheels and fitting them to the locomotive could screw up the gear hinges (Sun and Planet gear) that moved the train.
I never would have guessed it. I just figured the wheels were on the track.

The history of a “narrow guage” railroad from my childhood.