How to check a used tire before you buy: a 6-point inspection

You do not need to be a tire tech to weed out most of the bad used tires out there. Four of these six checks take a coin and a phone. The last two tell you which check you cannot do on your own. Run them in order.

1. Read the build date and set an age limit

Find "DOT" on the sidewall, followed by a run of characters that ends in four digits. Those four are the week and year it was built: 2321 is the 23rd week of 2021. (A three-digit code means it was made before 2000. Walk away.) Rubber ages from the inside even sitting in a warehouse, so many vehicle and tire makers say to replace tires at 6 to 10 years old regardless of tread (NHTSA); Michelin and Continental both cap it at 10. For a used tire, under 6 years from the build date is a sensible personal rule. Cannot find or read the DOT date? Walk away, because you cannot judge age by eye.

2. Measure the tread, do not eyeball it

In most states the legal worn-out point is 2/32 of an inch, but that is the "replace it now" line, not a buying target. Grab a penny and slot it in with Lincoln's head upside down; if you can see the top of his head, the tire is done (2/32"). A quarter is the better tool: if the tread reaches the top of Washington's head you still have at least 4/32", the level AAA and Consumer Reports suggest replacing at, since wet stopping distance climbs fast below it. Check several grooves and both edges. Uneven wear, one edge lower than the other or a cupped, scalloped surface, points to alignment or suspension trouble on the tire's last car.

2/32" is the floor, not the goal A tire worn to 2/32" can need nearly twice the wet stopping distance of a new one (Consumer Reports). Aim well above the legal minimum, especially for rain and snow.

3. Look for improper repairs

A proper repair is fine. A botched one can let go at highway speed. The industry standard (USTMA): a puncture can be fixed only in the tread area, no larger than 1/4 inch, with a combined plug and patch installed from inside the tire. Inside, a good repair looks like a round patch. Outside, watch for a plug with no patch behind it, any repair on the sidewall or shoulder, or several repairs bunched together. Any of those, pass on the tire.

4. Inspect the sidewalls, bead, and inner liner

Run a hand around both sidewalls, looking for cracks (dry rot), bulges or blisters (the internal structure has separated), cuts, and any spot showing fabric or steel cord. Check the bead, the edge that seats against the wheel, for damage. If you can see inside the tire, the inner liner should be smooth and whole, with no wrinkles, gouges, or a rubbery dust that hints the tire was run flat. Exposed cord or a bulge is an automatic no.

5. Look for punctures, and for uneven wear

You can find most air leaks without any air. Run a hand across the tread for a nail or screw head, look for a plug's rubber tail or the patch on the inside, and hold the tread up to the light if you can. A true pressure test means mounting the tire on a rim and inflating it in a safety cage, ideally with a soap or water-bath check, which is a tire shop's job at mounting time and not something you or a cash-and-carry seller can do off a pile.

Wear should also be even across the tread. Cupping, feathering, or one shoulder worn well past the other says the car it came off had an alignment or suspension problem, and a tire worn that way keeps wearing that way on yours.

6. Check the tire for recalls

Take the full DOT / Tire Identification Number and check it against nhtsa.gov/recalls or USTMA's lookup tool. Recalled tires still float around the used market because nothing yanks them out of it, so this one check catches a risk most sellers will not mention.

The check you cannot do in a parking lot

There is one limit you cannot get around. USTMA states that inner-liner and internal damage only become visible once the tire is demounted from the wheel, and that no inspection, even an expert's, can vouch for a tire's internal integrity. An old pothole, a curb strike, or a long stretch run underinflated can leave damage that never shows on the outside. So nobody can tell you a used tire "is safe." What a good seller can do is inspect it against a published standard, document the result, and publish that record with the tire. That is the whole idea behind the RealTreads Standard: it gets you as close to certain as anyone can without cutting the tire open, and it says exactly what was and was not checked.