I don't mean if you have damage or the tread is less than 2/32". I mean do you run your tires to a certain mileage, or to a certain tread depth, or ? Just for example, I have some tires that are guaranteed for 60,000 miles and I'm around 56,000 miles and they are generally OK looking. They've got enough tread to be legal, but I haven't measured it. They'll definitely be legal to 60,000 if I want to drive them that long. What is your criteria for getting new tires?