Many people use their vehicles to get from A to B and focus on getting there rather than how they arrive. In other words, the car is a tool and sometimes the finer details of vehicle operation are easy to ignore. Staying safe on the roads is important, but often we avoid simple maintenance tasks, such as basic tire care. Having proper tread depth on tires is one of the simplest forms of vehicle safety, and something all motorists can stay on top of with the tire penny test (which I’ll discuss in this article).
While there are several factors that could lead to needing to replace your tires, tread depth is one of the most obvious. Sure, it is always good to get a professional to measure your tread depth, but you can also do the measurement at home with the penny test.
Or can you? Well, the tire penny test is a known method for testing tire tread depth but is it legit, and how accurate is it?
In the following article, I will walk through how to check your tire tread with a penny, offer insight into how well it works (and its drawbacks), and I will also point to some other methods for measuring tire tread depth that may be more accurate and reliable.
Let’s get started.
So, What is the Tire Penny Test?
Before you can measure your tire thread depth, you need to know what a correct depth is and what indicates tire replacement is necessary. Tire treads are measured by 32nds of an inch in the United States. When you install a new tire, it will usually have either 10/32” or 11/32” tread depth. You may find SUVs and trucks have deeper treads than others.
The tire penny test takes advantage of the distance from the edge of the penny to the top of Abraham Lincoln’s head (2/32″), which is the minimum legal limit for tread depth for an automobile’s tire. When performing the tire penny test you hold the penny upside down in the tread of your tire. If you can see the top of Lincoln’s head, you need new tires.
Here’s how you perform the test:
- Get a penny coin and hold it between two ribs of the tire with Lincoln’s head facing down (upside down).
- If the tire tread covers a part of Lincoln’s head, the tread is still deep enough.
- If can see all the head of the 16th U.S. President, then the tread is too shallow and the tire needs replacing.
- Use the same method to check various parts of the tire because tire wear is usually uneven.
Is the Penny Test for Tires Accurate?
This is the million dollar question. Firstly, you may be wondering why we use a penny and not another type of coin. Well, the simple reason is because the space between the edge of the coin and Abe Lincoln’s head is 2/32”, the exact minimum thread depth according to the Department of Transportation.
However, there is obviously no room for error when doing the coin test. For example, holding the coin on an angle will give incorrect results. Still, as far as home solutions go, the penny test remains an effective way to gauge the depth of your tire tread.
Is There a Better Way to Check Your Tire Tread?
As you might expect, using a penny with Honest Abe’s head as a gauge is not the only way to evaluate your tire tread depth at home.
Tire Quarter Test
In recent years there has been a debate raging in the tire community and road safety industry around the validity of the guidelines. Some argue the Department of Transportation is too forgiving with its 2/32” mandate.
In 2007, Consumer Reports suggested 2/34” should be the low end threshold for tire tread depth. As reported by Dunn Tire, the reason for the suggestion is breaking distances in wet weather dramatically increase when the tread depth drops below 2/34”.
It is worth noting the recommendation comes from over 10 years ago. The Department of Transportation has not changed its requirements since then. You won’t be breaking the law by having treads of 2/32”, but there is some contention that 2/34” is a safer threshold.
If you do decide you want your tire treads to be no lower than 2/34”, we recommend using a quarter instead of a penny. You guessed it, the space between the top of George Washington’s head and the edge of the coin on a quarter is 2/34”. One thing is for certain, having more tread is better for road grip and vehicle safety.
Tread Depth Gauge (what is it and how to use it)
While the penny test is a decent way to check your tires have enough tread, using a dedicated tool is better. Not least because a proper tread depth gauge will tell you precisely how much depth you have and give you an idea of how much useful life the tire has remaining.
Tread depth gauges are measured by 32nds of an inch in the U.S. and often in millimeters in other countries. As a comparison, 32nds of an inch are equal to 25-26mm.
When you have a tire depth gauge, follow these steps to use it:
- Test the gauge by pressing it against a wall or solid surface. This ensures the tool compresses fully to zero.
- Insert the measuring scale into the gauge, pushing it as far as it goes.
- Put the probe inside a tire groove between two treads and push the base of the gauge.
- Remove the gauge while leaving the probe in place to see the tread depth.
- Repeat the process in other tire locations (inner/outer) and take an average of all readings.
Why the Depth of Your Tire Tread Matters
Tires are one of the most important parts of your car, and the chief safety feature. Tire treads create the grip that keeps your vehicle on the road during different speeds, varying surfaces, and differing weather conditions. Deeper treads mean more traction when driving, making collisions less likely to happen.
Risks of Driving on Worn or Bald Tires
Poor vehicle alignment, worn parts, incorrect air pressure, vehicle load/weight, driving surfaces, and regular usage can all cause uneven tire wear and worn treads.
Running your vehicle on bald or excessively worn tires puts the safety of you and other road users at risk. This is not a myth, with a study by the National Center for Statistics and Analysis at the National Highway Traffic Safety Administration showing 26.2% of road collisions involves vehicles with bald tires.
Driving with worn tires is dangerous, even on dry or excellent road surfaces. Add rain, snow, excessive speed, or poorly maintained roads into the mix and you have a recipe for an accident. Some of the main dangers of running a vehicle with bald tires include:
- Heat builds quicker, increasing the chances of a blowout.
- A layer of water builds more easily between the road and the tire, causing more risk of hydroplaning.
- Extreme difficulty handling in wet, icy, of snowy road conditions.
- Bald tires lose air faster, so it is likely the air pressure will be incorrect.
What is the Minimum Tire Tread Depth that Is Safe?
According to the U.S. Department of Transportation, motorists should replace tires when the tread depth reaches 2/32”. Depending on your state, it may be a legal requirement to change tires once they reach this depth. The penny test is a home remedy to check if your tires are still within the recommendations of the Department of Transportation.
While 2/32” is the legal requirement, the reality is the deeper your tire tread the better. That is why some road safety organizations suggest changing tires when the tread depth drops below 2/34”.
Do All Cars Have Tire Wear Bars?
While the penny test is good for checking the depth of your tire tread, you can also see a built-in solution on your tire. Federal Motor Vehicle Safety Standards (FMVSS) require tire manufacturers to include tire wear bars on all of their tires.
Tread wear bars or indicators are small, raised rubber bars that sit within the tread grooves of tires, typically at intervals around the tires. They are able to show how evenly a tire is wearing during its usage life. When the tread wears down to the level of the indicator bar, the tread on the tire (or a specific part) is below the legal limit and you need to replace the tire.
While the tread indicator bar is a handy component of your tire, it does not provide information about the tread depth on all parts of the tire. That is why we still recommend using the penny test or a tire depth gauge.
If Your Tire Tread Depth is Uneven What Does that Mean?
In most cases, you will not get an even level of wear across the whole tire. You may perform the penny test on one part of the tire and see the tread is perfect, while another part may be below the legal requirement. While it may be tempting to ignore this because the rest of the tire is fine, doing so is dangerous.
Uneven tire treads can cause problems with traction and put your life at risk when driving. Also, it is illegal in many states to run a vehicle with tire treads below 2/32”, even if it just parts of the tire that are worn.
How Proper Inflation Makes Your Tires Last Longer
Properly inflated tires that match the guidelines of your vehicle manufacturer can have numerous benefits.
You will get better fuel economy, experience superior vehicle handling, and even have a more comfortable ride.
In terms of tire wear, properly inflated tires allow tread to wear evenly. Over inflated tires usually cause greater wear in the center of the tire, while under inflation can cause premature wear on the edges of tires.
Why Rotation and Balancing Matter to Tread Wear
Your vehicle should be properly aligned at all times to provide a more balanced ride, handling experience, and promote even tire wear.
Even if your car has proper alignment, regular rotation of tires is recommended to maximize the tread life of your tires and get them to last for many miles.
Vehicle manufacturers usually include rotation schedule recommendations for individual models, usually around every 5,000 to 8,000 miles.
The Tire Penny Test: Easiest Way to Check Tire Treads?
There is no doubt that if you want a quick understanding of your tire tread depth, the penny test is an effective solution. As long as you hold the coin straight, you can get pretty accurate results from this test.
You can quickly see at home if your tire treads are becoming too worn and the tires need replacing. We recommend coupling the tire penny test with regular checks of the tire indicator bars.
Of course, buying a proper tire tread gauge will give you the most accurate results at home. Still, noting beats taking your vehicle into the shop regularly for a professional to run tests on your tires.