How Often to Replace Tires

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Like many other car maintenance tasks, when it comes to your tires, there is no exact number of years or miles you should reach before you replace them. How often to replace tires depends on a number of variables, including obvious considerations such as tread depth or sidewall damage, but it also depends on indicators you may not often think about, including tire age and the climate you live in.

Tires are an extremely important part of your car's equipment. No matter how many advanced driver assistance or safety systems your car has, worn-out or damaged tires can render them useless. Those four rubber hoops are the only part of an automobile that contact the road, and bad tires can cause your car to lose traction or efficiency and could lead to a loss of vehicle control entirely.

When to replace tires: Insufficient tread depth

As we said at the outset, there is no set of rules you can follow that will tell you exactly when to replace your tires. So how do you tell when your tires need to be replaced?

Knowing when to replace tires requires you to check on a number of factors, starting with measuring the depth of tread that's left on all four of your tires. The grooves that separate the tread blocks — the rubber bits that touch the ground — are an important part of a tire's design. As tires wear down, those grooves get smaller, and if they get too shallow, the tire will lose its ability to grip the road, particularly in wet, snowy or other slippery conditions. Most tire manufacturers and states consider tires worn out when they are down to the 2/32nds treadwear indicator. Depending on your circumstances, however, you might want to replace your tires sooner.

Many drivers over the years have relied on the penny treadwear test to determine if a tire is down to 2/32nds. It works like this: Hold a penny in your hand with Lincoln's head visible. Stick the penny into a few spots in the grooves of your tires. If Lincoln's head is fully or partially covered by the tire blocks outside of the grooves, there's still some life left. This is a time-honored test, but it's not the most accurate way to measure your tread depth.

According to AAA, a quarter is a more useful tool. Here are the instructions on AAA's website: "Insert a quarter into a tread groove with the top of Washington's head facing down. If the top of his head is not visible, your tires have at least 4/32" of tread and are fine for continued use. If you can see above the top of Washington's head, it is time to start shopping for new tires. Take measurements in three locations across the tire's tread: (1) outer edge, (2) center, and (3) inside edge."

Coins may be handy, but for a truly accurate measurement, consider using a tool designed specifically for measuring tire tread depth. Tire tread gauges are offered with both mechanical and digital readouts and can be used to get an exact measurement of your tire's tread depth.

If you don't have access to a tire tread gauge or an appropriate coin, you can still check your tires for wear using the treadwear indicators that are molded directly into your tire's grooves. Popular tire brands such as Michelin, Goodyear, Pirelli, Cooper and pretty much all others include built-in treadwear indicators that gradually appear or disappear as a tire wears down. By locating and inspecting these indicators, you can check how much tread life is still left on your tires.

When to replace tires: Mileage

All tires come from the manufacturer with a treadwear rating, and many include warranties for as few as 20,000 or as many as 100,000 miles. These warranties can help you know how many miles you might expect from a new set of tires, but this mileage figure isn't the only number you should focus on when tracking at what point you should replace tires.

Since 1979, all tires sold in the United States have a Uniform Tire Quality Grading (UTQG) that's defined by the Department of Transportation and National Highway Traffic Safety Administration. Part of the UTQG is a treadwear rating that should be between 100 and 1,000. Since a rating of 800 is twice as high as a rating of 400, the 800-rated tire should last twice as long. These numbers are assigned by the tire manufacturer, so it's difficult to compare one brand with another based solely on the UTQG.

No matter what a manufacturer claims for warranty purposes or what a tire's UTQG rating may be, if it's worn down past 2/32nds — or earlier if you go by AAA's recommendations —  it should be replaced.

When to replace tires: Damage to the tread or sidewalls

Sometimes it's obvious when there's damage to your tires. If you run over a sharp object such as a nail or screw, you may slowly lose pressure in your tires, or you may hear a constant tapping sound when the object comes into contact with the road surface as the tire spins. Other damage may not be so clear.

It's important to regularly inspect your tires for damage. Checking your tire tread may require you to move the car a few times so you can get a look at the tire's entire circumference. Check the sidewall for any cracks, scrapes or bulges. If you're not sure if there's tire damage, consider taking your car to a tire shop or mechanic for inspection.

While you're checking your tires for damage, you should also look for uneven wear patterns. A car with poor alignment or some other problem may cause one tire to wear faster than others, or it could cause one part of a single tire to wear while the rest of the tire seems fine. Similarly, improper tire pressure can cause uneven wear, possibly in the center if it's overinflated or on the edges if it's underinflated. Even if only one part of your tire is below the wear threshold, that entire tire needs to be replaced.

When to replace tires: Age

Since tires are made from rubber, steel belts, and additives and compounds that improve traction, they always wear out with age. Even if a tire has plenty of tread depth, it's vital to check the tire to find the date it was manufactured. This is especially true if you live in an area with extremely hot temperatures or live near one of the coasts.

For an in-depth discussion on tire age, check out Edmunds' article on old and dangerous tires. In brief, tires that are too old may start to crack, or, in extreme cases, the tread can separate from the rest of the tire. If this happens, the results can be deadly.

Ford recommends replacing tires every six years regardless of how much they've worn or how many miles they've been driven. Michelin suggests checking your tires thoroughly every five years and replacing them no matter what every 10 years.

It's not as easy as it should be to determine how old a tire is. This Edmunds article about reading a tire's sidewall explains all the specifics, but tires produced after 2000 (which should cover nearly every tire that's still on the road today) will have a four-digit code, while older tires have a three-digit code. Either way, it's good practice to keep track of the age of the tires on every car you own and drive.

How long should tires last on average?

If you've made it this far into the article, you probably already know that there's no exact period of time that your tires will last. Organizations like Consumer Reports that test tires on a regular basis can offer guidelines on the life expectancy of a new set of tires. Similarly, online tire outlets like TireRack.com often offer ratings and owner reviews of popular tires.

It's also worth remembering that a tire's wear rating or mileage-based warranty is just one of the factors you should take into consideration when it's time to buy new tires. The climate you live in, the type of car you drive, the types of conditions you encounter while driving, and, of course, cost are all important parts of the decision-making process when buying tires.