It also depends on the make and where you live. I stretched my Yokohama's out to ~80k miles with good tread still left when I replaced them. But I live in the southern part of the US, so we don't have to deal with snow and ice cycles that cause tires to wear faster.
Of course, I inspect my tires weekly looking for sidewall damage, dry rot, and other various deformities. I also rotate my tires fairly frequently (every 8-10k miles usually coincides with oil change)
It also depends on the make and where you live. I stretched my Yokohama's out to ~80k miles with good tread still left when I replaced them. But I live in the southern part of the US, so we don't have to deal with snow and ice cycles that cause tires to wear faster.