flat tire cause of 100 years ago that we don't have to worry about anymore

Horseshoe nails.

I know I've posted a couple times about the many spare tires early cars carried, and the different ways that tires were patched.

I never thought about what caused those flat tires, I assumed it was rough roads, rocks, and sharp stones... but of course when horses were still common on roads, the loose horseshoe nails would have been a frequent cause of flats.

just one of the things that made me say Hmmm.