Tires are the only part of your car that actually touches the road, which makes them one of the most important safety components you own — and one of the easiest to neglect until it is too late. This guide covers how to tell when tires are worn out, how to read the confusing numbers on the sidewall, whether you should buy two tires or four, and what a new set typically costs.
The short version
Replace tires when tread wears to the legal limit — or sooner for wet-weather safety.
The penny test and built-in wear bars both tell you when tread is too low.
Tires also age out: replace old tires even if the tread looks fine.
Buying all four keeps handling balanced; two is a compromise if the others are good.
A set of four commonly runs $500 to $1,400+ mounted, depending on size and quality.
When to replace your tires
Tread depth
New tires start with plenty of tread; as it wears down, they grip less — especially in rain and snow. The classic penny test: insert a penny into the tread with the head upside down. If you can see the top of the head, your tread is dangerously low and it is time to replace. Most tires also have molded wear bars that become flush with the tread surface when they are worn out. Many drivers replace before the absolute legal minimum for better wet-weather safety.
Age
Tires degrade with time, not just miles. Rubber hardens and cracks over the years, which reduces grip and raises the risk of failure — even on a tire that looks barely used. Many manufacturers suggest considering replacement once tires reach several years old regardless of tread, and inspecting them closely as they age. You can find the manufacture date on the sidewall.
Damage and uneven wear
Bulges, deep cuts, persistent slow leaks, or exposed cords mean replace now. Uneven wear — one edge worn more than the other, or a cupped pattern — points to alignment, suspension, or inflation problems that should be fixed so your new tires do not wear out the same way.
How to read the sidewall
That string of numbers and letters looks cryptic but follows a standard format, for example P225/65R17. Here is what the main parts mean.
Part
Example
Meaning
Width
225
Tread width in millimeters
Aspect ratio
65
Sidewall height as a percent of width
Construction
R
Radial (the common type)
Wheel diameter
17
Rim size in inches
Your correct tire size is also printed on a placard, usually in the driver’s door jamb, along with the recommended inflation pressure. Match the size (and load and speed ratings) when you replace, unless a tire professional recommends a proper alternative.
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Two tires or four?
Replacing all four at once keeps grip and handling balanced, which is ideal — and on all-wheel-drive vehicles it is often required to avoid drivetrain strain, since mismatched tire diameters can damage the system. If your budget only allows two, that can work when the other two still have plenty of tread and match reasonably well; the new tires generally go on the rear for stability. When in doubt, ask the shop, and mention if you have all-wheel drive.
Pro tip — rotate and inflate to make tires last
The cheapest tire savings is making the ones you have last. Rotate them on schedule (often every oil change or two) so they wear evenly, keep them at the pressure on the door placard, and get an alignment if you notice pulling or uneven wear. Proper care can add thousands of miles of life to a set.
What tires cost
Prices vary widely with size and quality. A set of four for a common sedan, mounted and balanced, commonly runs from around $500 to $1,400 or more in 2026; large truck, SUV, and performance tires can go higher. Beyond the tires themselves, expect charges for mounting, balancing, new valve stems, and disposal of the old tires. Buying a matched set from a reputable installer, plus an alignment when needed, protects the investment.
Time for new tires?
Find a tire and repair shop near you on Mechanics At Your Service.
Use the penny test — if the top of the head shows when you insert a penny upside down, the tread is too low. Also look for the built-in wear bars becoming flush with the tread. Many drivers replace a bit before the legal minimum for better wet grip.
Do tires really expire?
Yes. Rubber hardens and cracks with age, reducing grip and raising failure risk even if the tread looks fine. Check the manufacture date on the sidewall and consider replacement as tires reach several years old, inspecting them closely along the way.
Can I replace just one or two tires?
Sometimes. If the others still have good, matching tread it can be fine, and new tires usually go on the rear. But all-wheel-drive vehicles often need all four matched to avoid drivetrain damage. Ask the shop and mention your drivetrain.
Why are my tires wearing unevenly?
Uneven wear usually points to alignment, suspension, or inflation issues. Fix the underlying cause when you replace the tires, or the new set will wear out the same way. Regular rotation and correct pressure also keep wear even.
General information for car owners — not professional automotive advice. Repair needs, costs, and part prices vary by vehicle and location; confirm with a licensed mechanic.
