When is the right time to change car tires?

dogpile.com before asking here

I've never used the penny wear test before, I just observed it with my eyes. Thanks @ Elvis Telecom and everyone. I found out this article about the penny used to check the tread depth, https://tireer.com/penny-tire-test/ it is really helpful for me right now.

Always check your tyres before you drive. There should be about four.