How long will a used tire last?
How to work out the miles left in a used tire from its tread depth, and what shortens it.
Work it out from the tread
A tire is legally worn out at 2/32. So the tread you are buying is whatever it has now, minus 2/32.
A tire with 8/32 has 6/32 of usable tread left. One with 5/32 has 3/32 left, or half as much. That ratio is the honest way to compare two used tires.
Turning 32nds into miles
There is no fixed number of miles per 32nd. It depends on the tire, the car, the roads and how you drive.
What you can do is compare. A tire with 6/32 of usable tread has twice the life of the same tire with 3/32. If you know roughly how long your last set lasted, you can scale from that.
Tire makers publish treadwear warranties on new tires, which give a rough idea of how fast a given model wears. A harder-wearing touring tire will go further per 32nd than a soft performance tire.
What shortens it
Running the tires under-inflated wears the shoulders and wastes tread fast. Check the pressure on the door sticker, not the number on the sidewall.
Wheels out of alignment wear one edge away while the rest of the tread looks fine.
Hard cornering, heavy loads and hot roads all take tread off quicker.
Age matters too
Rubber hardens as it ages whether you drive on it or not. A tire with deep tread but ten years on the clock is not a bargain.
The last four digits of the DOT code on the sidewall are the week and year it was built. 2321 means the 23rd week of 2021. You can read that code in the sidewall photo on every listing here.
The short version
Buy on usable tread, not total tread. Check the date code. Keep the pressures right and the alignment straight, and a good used tire will see out most of the life it has left.