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December 20, 2020

How to Test with a Penny or a Quarter

If you own a car, you're probably familiar with basic maintenance and safety checks that can improve your car's performance without requiring a trip to the auto shop. One big focus of routine maintenance is the condition of your tires, which can include managing tire pressure, knowing how to spot or change a flat tire, and determining if it's time to purchase new tires.

Even if you're uncomfortable changing a flat or even checking tire pressure on your own, tread depth is something that anyone can measure. Thanks to a nifty, widely used penny trick, tires and their tread can be easily checked in just a few seconds. Read on to learn more about the penny tread test, as well as a newer test that replaces pennies with quarters.

Penny and Quarter Tire Test

The Importance of Proper Tread on Tires

The concept behind both the penny tire test and the quarter tire test is based on using tire tread depth to gauge tire performance. While there are other factors involved in the overall performance of a tire, including internal tire pressure or cracks along the sidewall, tread directly correlates to your vehicle's ability to gain and maintain traction on the road. This is especially important to check when slippery conditions like rain, snow, ice, or even loose gravel exist.

Unlike tire pressure, you can't adjust the depth of tire treads over the life of your tires. These treads wear down with use, and as the tires smooth over, they present an increased risk of slipping on roadway surfaces. For this reason, drivers should be vigilant of the miles driven on their tires, as well as their own wear and tear. The use of simple tire coin tests provides an easy option to measure tire tread depth at home and can be done as frequently as needed to prevent those bad conditions. 

How to Conduct the Tire Tread Penny Test

The penny tread test is simple and is based on a commonly used tire tread measurement to identify tires that need to be changed. Conventional wisdom suggests that, in good driving conditions, tire treads should be at least 2/32nds of an inch deep. On a U.S. penny, 2/32nds is also the same distance between the top of President Lincoln's head and the edge of the penny.

To check tire tread with a penny, stick the edge of the penny in between your tire’s treads. Make sure President Lincoln's head is pointed toward the tire. When the coin is between the treads, look from the side to see if the top of President Lincoln's head is visible. 

  • If the top of his head isn't visible, this means your tire tread is more than 2/32nds of an inch, and you may be able to drive farther on your tires before swapping them out.
  • If the top of his head is visible, this means your tire tread is less than 2/32nd of an inch and may be unsafe to drive on. At this point, tire experts recommend that you visit a tire shop to replace these worn tires with a new set.

If you check tires with a penny and you can see the top of Lincoln's head, that might not mean you’re safely out of the blue, though. Try the quarter test next. 

Using the Quarter Tire Test

The penny tread test has been a longstanding trick to quickly measure tire tread and evaluate the health of your tires. In recent years, though, tire experts have cautioned that there's a problem with this test: by the time you check tires with a penny and discover that the tread depth is less than 2/32nds of an inch, you're already driving on smooth tires that present a safety risk.

This is especially true in inclement weather, where road conditions are less than ideal. To ensure that car owners are changing their tires before the treads become a safety issue, some tire experts now advocate for what's called the quarter tire test. 

This test is performed the same way as a penny, pressing the edge of a quarter into the tire tread to compare the height of the treads to the head of President Washington on the U.S. quarter. The difference in this test is that, on the quarter coin, the top of President Washington's head is about 4/32nds of an inch from the edge of the coin—double the distance of a penny.

With this measurement, drivers can check their tread and identify depths that fall below 4/32nds of an inch, at which time it's wise to consider a tire replacement in the near future. But even when that tread depth falls below the 4/32nds of an inch mark, tires still offer a good measure of performance and safety, which means you aren't at immediate risk of wrecking your vehicle on threadbare tires.

While these tire tread tests are simple, they're very effective at gauging tread depth and simple enough for any driver to use. If your tire coin test reveals tire treads that have worn thin, contact your local tire shop near you to outfit your vehicle with some brand-new replacements.

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