What Is the Tire Penny Test?
The Lincoln tire penny test is a method of testing the tread depth of tires using something you probably already have lying around the house: a penny! It requires no other tools or supplies and only takes a couple minutes from start to finish. You simply insert the penny into the treads of your tires to use Lincoln’s head as a measurement gauge for the tread depth. We’ll explain how to do this correctly in more detail later on in this article.
The tire penny test is an extremely easy car maintenance trick, so it’s often the first thing that new car owners learn to do themselves. It’s also really important to maintain the tread depth of your tires, as we’ll explain in the next section, so being able to do the penny test is a simple skill worth knowing.
Why Tread Depth Is So Important
If you’re reading this article, you might be wondering why knowing how to do an accurate, reliable tire tread depth test like the Lincoln tire penny test is so crucial. It’s because maintaining sufficient tread depth is very important in order to maintain the proper functionality of your tires and, by extension, of your car as a whole.
It’s really a matter of safety: if your car’s tires lack depth, your car will lack traction on the road and you and your passengers will be endangered, especially when roads are wet or icy.
More specifically, “worn tires are less able to channel water [than new tires] and the risk of hydroplaning increases, especially at higher speeds,” according to Driving Press. Overly worn tires also put you at higher risk of punctured tires and “sudden blowouts,” which by extension increase the possibility of losing control of the car (especially if you’re driving quickly).
What Is The Tread Depth Of A New Tire?
For starters, it’s important to know that the standard method for measuring tread depth in the U.S. is to use units of 1/32nd of an inch. Perhaps that number doesn’t mean much to you yet because it is so abstract and hard to imagine–for reference, the tread depth of a new tire is usually about 10/32” or 11/32”. This isn’t universal, however, as winter tires and the tires of SUVs and trucks often have deeper treads to give them extra traction for their specialized applications.
At What Tread Depth Should You Replace Tires?
Over time, thousands of miles’ worth of friction on the pavement (and other road surfaces of varying smoothness) inevitably wears away the tread ribs of any tire. Eventually, no matter how carefully you care for your car and its tires, you will have to replace the tires once the tread depth reaches a certain threshold of shallowness.
What is the specific threshold? According to the U.S. Department of Transportation (DOT), the foremost authority on the subject, your tires should be replaced once they’ve reached a tread depth of 2/32”. Depending on what state you live in, you might very well be required by law to observe this piece of DOT advice.
Keep in mind that this 2/32” rule is a bare minimum and does not always apply. For instance, you may want to replace your tires well before they reach a 2/32” tread depth if you frequently drive on wet roads. In this situation, it may make more sense to replace your tires when they reach 5/32”.
In addition, tread depths of 4/32” or less are considered a safety hazard at which point tires are functionally bald in the winter, especially if you often contend with snowy or icy weather. The experts at Bridgestone Tire point out that “tire performance can diminish significantly before your tread hits 2/32”. Even though the law deems [it] fit for safe driving [it] may not prevent you from hydroplaning or losing control in rainy, slushy conditions.”
It can never hurt to replace your tires sooner, so we would strongly recommend erring on the side of caution if you have any concerns about your tires’ tread depth.
How to Check Your Tread Depth with the Penny Test
Luckily, the penny test is quite straightforward. In fact, perhaps the most challenging part of doing this test is remembering which direction to insert the penny into the tire treads. Driving Press recommends using the following rhyme to remember the correct positioning: “Head into the tread.” This means that when you place the penny, make sure that Lincoln’s head is facing toward you and is upside down.
Once you’ve done that, how do you assess the results of your penny test? Simply put, if your tires have enough tread, you won’t be able to see the top of Lincoln’s head. It doesn’t matter if you can see the rest of his head and face, as long as the top of his head is concealed.
But if you can see Lincoln’s entire head, you can be certain that your treads are much too worn down and have 2/32” of tread (or even less!) left on them. If this is the case, this means your tires are close to bald and must be replaced as soon as possible.
Some tips to ensure you do the penny test correctly
A 32nd of an inch is an extremely small unit of measurement, so it’s important to do the penny test correctly to get accurate results. Here are a few additional tips to keep in mind before you attempt the penny test yourself.
For starters, keep in mind that when you do this, you really have to check all four tires. You should be focusing in particular on the areas of the tires that are visibly well-worn. In addition, if there are parts of your tires that pass the tire penny test and others that fail, your tires as a whole have failed.
For instance, if the most worn areas of your tires have a tread depth of 2/32” but the least worn areas’ tread depth is a less dire 5/32”, you still need to replace your tires. (Also, if you have quite a bit of uneven tread wear, you might have a problem with your car, such as wheel misalignment or tires that have been inflated incorrectly.)
As an additional disclaimer, Driving Press notes that “many drivers do not know that the penny test may not reflect all legal requirements for tread depth. In fact, by the time you can see all of Lincoln’s head, your treads have worn low enough that your tires are in violation of safety laws and in need of immediate replacement.”
The tire penny test isn’t perfect. Although it is a quick way to see if your tires are in dire need of replacement, checking your car’s tread wear indicator bars (if it comes with them) or using an actual specialized tool like a tread depth gauge might make more sense if you’re concerned about accuracy.
Finally, as with just about every automobile-related concern that has safety consequences, you should have your tires looked at by a licensed mechanic if you don’t feel confident measuring their tread depth yourself, or if there’s anything else you’re uncertain about.