Monday, July 22, 2024

How to Check Tire Tread Depth: The Penny Test Has The Answer


Tread depth is one of the most important maintenance checks for your tires. It measures how much tread is left on your tires in 32nds of an inch. Having sufficient tread depth is crucial for maintaining traction, braking performance, and handling in wet or snowy conditions.

As tires wear down over time and their tread depth decreases, they become more likely to hydroplane or skid across wet roads. This greatly increases the chance of losing control or being unable to stop in emergency braking situations.

To help drivers easily monitor their tread depth at home, the penny test was developed. This simple technique only requires a penny and enables you to approximate when your tires may need replacement without specialized tools.

The penny test takes advantage of the fact that tread on most tires should cover Abraham Lincoln’s entire head on a penny inserted into the tread. If any part of Lincoln’s head is visible, your tread depth may be insufficient and putting you at risk on wet roads.

This article will explain what tread depth is, the dangers of driving with inadequate tread depth, when to check it, and provide a step-by-step guide to safely performing the penny test.

We’ll also cover the advantages and limitations of relying on the penny test before discussing when to replace tires.

With this knowledge, you can easily incorporate the penny test into your regular tire maintenance routine. Ensuring proper tread depth will keep you and your passengers safe in all driving conditions.

What is Tread Depth?

Tread depth refers to the grooves on your vehicle’s tires that provide traction. As the tires wear down over time and with use, these grooves become shallower. Tread depth is a measurement of how deep the grooves remain.

Most states require a minimum tread depth of 2/32 inch for front tires and 4/32 inch for rear tires.

Tread depth can be measured in millimeters or using the 32nds system. In millimeters, the minimum is usually 1.6 mm for front tires and 3 mm for rear. In the 32nds system, tread depth is measured in 1/32 inch increments.

So 2/32 inch is the minimum for front tires, and 4/32 is the minimum for rear.

Proper tread depth is crucial for safe driving. Shallower treads mean less traction, longer stopping distance, and increased risk of hydroplaning on wet roads.

Checking and monitoring your tires‘ tread depth regularly ensures they remain above the legal and safety limits.

Dangers of Insufficient Tread Depth

Driving on tires with insufficient tread depth can pose serious safety hazards. As tire tread wears down, traction is reduced, especially in wet conditions.

This can lead to longer stopping distances, increasing the risk of accidents. Vehicles with worn treads will take longer to slow down and come to a halt when brakes are applied.

Insufficient tread also makes a vehicle more prone to hydroplaning or aquaplaning. This occurs when a layer of water builds up between the tires and road surface, leading to a loss of contact and control.

The grooves on tire treads help channel water out from under the tires. As the tread depth decreases, tires lose their ability to effectively siphon water.

Worn treads significantly diminish handling and cornering ability as well. The shallower tread provides less grip and stability when turning.

This makes it much easier to lose control in inclement weather and increases the chances of skidding or fishtailing.

Overall, driving with inadequate tread depth is extremely unsafe. The reduction in traction and braking performance leads to a much higher risk of crashes, especially in wet conditions.

It’s critical to regularly check tread depth and replace tires promptly once they near the minimum legal and safety limits.

When to Check Tread Depth

It’s important to check your tires’ tread depth regularly, such as every few months or before long road trips. Don’t just wait until your tires seem badly worn to inspect them. Here are some good times to check tread depth:

  • Regular intervals (every few weeks/months) – Get in the habit of checking tread depth regularly, such as every couple months or with each oil change. Consistent checks allow you to monitor tread wear over time.
  • Before long trips – Inspecting tread depth before embarking on a long journey helps avoid getting stranded with unsafe tires. Driving long distances at high speeds accelerates tread wear.
  • When tires seem worn – If you notice your vehicle seems to hydroplane more easily, tires are noisy, or your vehicle pulls to one side, check for insufficient tread. Visually inspecting for wear is not as accurate as measuring depth.
  • After punctures/repairs – Any tire damage can accelerate wear in that area. Re-check tread depth after plugging a hole or patching a puncture to ensure the tire remains roadworthy.

Getting in the routine of periodically checking tread depth takes only minutes and helps keep your vehicle safe. Remember to check all tires, not just the easiest to access. Consistent inspections allow you to replace tires before they become dangerously worn.

Using a Tread Depth Gauge

A tread depth gauge is a simple tool that allows you to precisely measure the remaining tread on your tires. Using one is straightforward:

  • Locate the tread wear indicators around the tire. These are small horizontal bars built into the bottom of the tread grooves.
  • Insert the probe end of the depth gauge into several tread grooves around the tire. Push it in firmly until it stops, which ensures you are measuring to the full depth.
  • Check the measurement on the graded scale. Most gauges will clearly indicate when you have reached 2/32nds of an inch tread remaining. This is the minimum legal and recommended depth for safe driving.
  • Compare measurements around the tire. Significantly uneven wear indicates improper inflation or alignment.
  • Record the lowest measurement. This is the tread depth value you should use to assess the tire’s condition.

Tread depth gauges provide much more accuracy than simple visual inspections or the penny test. Most measure in precise 1/32 or 1/16 increments.

This allows you to monitor more incremental tread loss over time. It also avoids inaccuracies from eyeballing or using an irregular coin.

For these reasons, a quality tread depth gauge is the best tool for routinely checking your tires. While the penny test has merits for convenience, a gauge is essential to determine when to replace tires based on absolute minimum tread depths. Investing in your own helps ensure you know exactly how much usable tread remains.

Performing the Penny Test

The penny test is a simple way to check your tire’s tread depth using just a penny. Here is how to do it:

  1. Take a penny and hold it with Abraham Lincoln’s head upside down and facing you.
  2. Select a point on your tire’s tread where the tread appears the lowest. This is usually near the center of the tire.
  3. Insert Lincoln’s head into one of the grooves of the tread, making sure his head is completely enclosed by the tread.
  4. If you can see all of Lincoln’s head, your tread depth is below 2/32 of an inch and your tires need to be replaced.
  5. If the tread covers part of Lincoln’s head, you have more than 2/32 of an inch of tread left. But it’s still a good idea to regularly check it going forward.
  6. Repeat this process around the circumference of the tire to make sure the tread depth is sufficient at all points on the tire.

The minimum recommended tread depth is 2/32 of an inch. This is the level at which traction is severely decreased on wet roads. If you can see all of Lincoln’s head when you perform this test, that means your tread depth is less than 2/32 of an inch and your tires are unsafe to drive on. They will need to be replaced.

Advantages of the Penny Test

The penny test has several key advantages as a quick and easy way to check your tires’ tread depth:

  • Simple – No special tools or equipment needed. Just find a penny in your pocket or purse and you’re ready to test. Extremely straightforward procedure.
  • Fast – Can check all tires in less than a minute. Much quicker than using a tread depth gauge.
  • Inexpensive – Only requires a penny, which you likely already have on hand. Saves money compared to buying a tread gauge.
  • Can be done anywhere – All that’s needed is a penny and your tires. Can perform it in a parking lot, at the gas station, or in your own driveway.
  • Gives general indication of tread depth – While not precise, inserting the penny into the tread grooves gives you a good approximate measure of how much tread is left. It’s accurate enough for a basic check.

The main appeal of the penny test is that just about anyone can do it at any time without any special tools or know-how. While it won’t give you an exact measurement, it serves as a quick and free way to periodically check on the remaining tread depth of your tires. Done regularly, it can alert you when your tires are getting dangerously worn and are ready to be replaced.

Disadvantages of the Penny Test

The penny test has some drawbacks compared to using a tread depth gauge:

  • Not as precise as gauge – The penny test only tells you if the tread depth passes or fails. It doesn’t give you an exact measurement like a gauge does. This makes it harder to monitor your tire wear over time.
  • Only tests one area of tread – The penny test just measures one small spot on your tire’s tread. But the tread depth may vary across different parts of the tire. A gauge allows you to check multiple spots around the tire for a more complete picture.
  • Doesn’t give measurement – Without an actual measurement, you don’t know if your tread is right at the minimum legal limit or has ample depth remaining. A gauge’s measurements can help you determine if you need new tires soon or if they still have some life left.

The penny test is quick and convenient. But for maximum accuracy, a dedicated tread depth gauge is a wise investment for safety. It provides precise measurements across your tire’s tread to determine if it’s time for replacement.

When to Replace Tires

If your tires fail the penny test, it’s time to measure the tread depth across the entire tire using a tread depth gauge. The legal limit for tread depth varies by state, but is typically 2/32 of an inch. If your tires are below this limit, they need to be replaced immediately.

However, it’s recommended to replace your tires even before they reach the legal limit. As the tread wears down, traction, braking, and handling are compromised. Most experts suggest replacing tires once they reach 4/32 to 5/32 of an inch of remaining tread depth. At this point, the performance and safety of the tires have started to diminish.

Replacing tires early helps maintain optimal traction and braking in wet or snowy conditions. It also allows you to replace tires on your own schedule, rather than scrambling when they become unsafe or illegal. Considering the importance of safe tires, it’s worth replacing them once the tread depth reaches 4/32 or 5/32 of an inch, even if they haven’t reached the legal limit yet.


Regularly checking your tires’ tread depth is an essential part of vehicle maintenance and road safety. As discussed, insufficient tread depth can seriously compromise traction, braking distances, and handling in wet weather and emergency maneuvers.

Although traditional tread depth gauges provide precise measurements, the penny test is an easy, convenient way for drivers to quickly check if their tires pass the minimum legal and safety requirements.

To perform the test, simply insert a penny into the tread with Lincoln’s head upside down and facing you. If you can see the top of Lincoln’s head, your tread depth is less than 2/32 inches and your tires should be replaced.

If the tread covers Lincoln’s entire head, you have at least the bare legal minimum of 2/32 inches, but it’s ideal to replace tires around 4/32 to 6/32 inches for maximum wet weather performance.

While the penny test has its limitations in terms of precision, it’s an invaluable tool every driver should use, especially before long trips or when buying used tires or vehicles.

Remember to check multiple points around each tire and make it part of your regular tire maintenance routine. Checking tread depth takes only seconds but gives you peace of mind and could help prevent an accident. Drive safely!

The Tire Reviews Team
The Tire Reviews Team
Rev up your knowledge with The Tire Reviews, your one-stop pit stop for swift and concise tire reviews. We cut through the noise, delivering the lowdown on treads that matter. Whether you're chasing performance or seeking a smooth commute, join us as we navigate the world of tires.

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