Tires are the only part of your car that actually touches the road, which makes them the single most important safety component you own. And yet they are easy to neglect, because a worn tire looks fine until the day it doesn’t grip in the rain or lets go on a cold morning. Knowing when to replace tires (by both tread depth and age), how to read the DOT date, and what to look for on a used car can keep you safe and save you from buying a car that needs $600 of rubber the week you drive it home.

Here is what actually matters, minus the marketing.

Compare tire sizes in our tire size calculator - check diameter difference and speedometer error.

When to replace: tread depth

Tread channels water out from under the tire. As tread wears down, wet grip falls off a cliff and the risk of hydroplaning climbs.

Tread depth is measured in 32nds of an inch. New tires start around 10/32 to 12/32.

2/32 inch is the legal minimum in most US states, and the point at which the built-in wear bars become flush with the tread. But this is a bare minimum, not a “still good” mark.
4/32 inch is a smarter replacement point, especially in a rainy climate, because wet performance has already degraded significantly by then.

The penny test: insert a penny into the tread groove with Lincoln’s head upside down and facing you. If you can see the top of Lincoln’s head, you are at or below 2/32 and the tire is done. The quarter test is stricter: if you can see the top of Washington’s head, you are below 4/32 and should start shopping.

Also watch for uneven wear: wear on one edge points at alignment or worn suspension (see suspension wear); center wear means over-inflation; both edges means under-inflation. Cupping or scalloping suggests worn shocks or unbalanced tires.

When to replace: age and the DOT date

Here is what most people miss: tires expire by age even if the tread looks fine. Rubber hardens and cracks over time, losing grip and becoming prone to sudden failure. Most manufacturers recommend replacing tires at 6 years regardless of tread, and treating 10 years as an absolute maximum.

You find the age in the DOT code on the sidewall. Look for “DOT” followed by a string of characters ending in a four-digit number. Those last four digits are the week and year of manufacture:

“2319” means the 23rd week of 2019.
“0524” means the 5th week of 2024.

So a tire with plenty of tread but a code reading “3115” (31st week of 2015) is over a decade old and should be replaced no matter how it looks. This matters enormously on used cars, spare tires, and cheap “new” tires that have sat in a warehouse for years.

Also inspect the sidewalls for cracking (dry rot), bulges, or bubbles. A bulge means internal damage and the tire can blow out; replace it immediately.

All-season, summer, and winter

All-season tires are the default in much of the US: a compromise that handles dry, wet, and light snow adequately, but excel at none. Fine for mild climates.
Summer (performance) tires grip best in warm, dry, and wet conditions but harden and lose grip badly below about 45 F. Not for snow.
Winter tires use a softer compound and aggressive siping for real cold and snow. If you get genuine winters, a set of dedicated winter tires outperforms all-seasons dramatically. Look for the three-peak-mountain-snowflake symbol for true winter rating; “M+S” alone is a weaker mud-and-snow marking.

Match all four tires as a set where possible, and never mix wildly different types across an axle.

Cost (USD)

Budget tires: $80 to $130 each.
Mid-range/name-brand: $130 to $250 each.
Performance or large SUV/truck tires: $200 to $400+ each.
Mounting, balancing, and disposal: $20 to $40 per tire.
An alignment after new tires: $80 to $150, worth doing to protect the new rubber.

Budget for a full set at replacement time; mixing badly worn and new tires upsets handling.

What it means when buying a used car

Tires are a fast, honest read on a used car:

Check tread depth with the penny/quarter test on all four. A car needing tires soon is a $400 to $1,200 expense to price in.
Read the DOT date on each tire. Old tires with good tread are still due for replacement, and mismatched dates suggest piecemeal replacement.
Look at wear patterns. Uneven wear is a clue to alignment or suspension problems, which are bigger and more expensive than the tires themselves.
Check that all four match in brand, type, and size. Odd tires can signal cheap fixes or past damage.
Inspect for bulges and sidewall cracks.

A pre-purchase inspection app like MotoPPI includes a tire walkaround that prompts you to check tread, DOT dates, and wear patterns, so uneven wear that hints at suspension trouble gets flagged too. See how to inspect a used car. And because tires are a predictable running cost, factor them into your budget using our cost of owning a used car guide.

The bottom line

Tires wear out two ways: by tread and by age. Use the penny and quarter tests for depth, and read the DOT code so a good-looking but decade-old tire doesn’t fool you. Match your tires to your climate, and treat uneven wear as a symptom of something else. When buying used, worn or aged tires are both a cost to negotiate and a window into how the car was cared for.