Tire Tread Depth: Why It Matters and How to Measure It
The tread on your tires is a crucial piece of driving safety and performance. All of those knobs, shapes, patterns and grooves have a combined purpose. They give the tire its ability to grip the road, accelerate, brake and corner — and even help maximize fuel economy. As the rubber on the tread wears away, so does the tire’s effectiveness. Keeping an eye on your tire’s tread depth is a vital part of routine vehicle maintenance.
What is tread depth?
Tread depth is a vertical measurement from the top of the tire’s rubber to the bottom of the tire’s deepest grooves.
As you drive on your tires, the rubber that makes up the tread — and the very thing that gives you traction — wears down. Over time, your tires will become less effective at gripping the road. Tires can lose their footing long before they're worn out, and, if a tread has worn down too far, they could become a serious safety issue.
The trick is to not let it get to that point.
Tread depth by the numbers
The tire industry standard for tread depth in the United States is measured in one thirty-second of an inch (1/32") increments (millimeters are used in countries observing metric standards).
New tires typically start with a tread depth of 10/32" to 12/32", with some off-road tires topping 15/32". New tire tread depth is the measurement typically published by tire manufacturers, but it’s not the same as usable tire tread depth. Most states and tire manufacturers consider tires to be bald when one or more of their grooves are worn down to 2/32". So, if you start with a new tire tread depth of 10/32", the actual usable tread depth is 8/32".
When tires wear down to 2/32", they’ve reached a point at which they’re unable to meet the challenges associated with driving on wet, slushy or snow-covered roads. They also become prone to heat damage in hot weather and are susceptible to flats, punctures or complete failure due to any or all of these hazards. In other words, when a tire’s tread depth is 2/32", it’s time to get new tires. Don’t wait.
For those who frequently drive in rain or snow, you may want to consider shopping for new tires for your car or truck when the tread depth is closer to 4/32".
How to measure tread depth
Measuring tread depth regularly is a simple and effective way to help ensure that your tires can still grip and stick to the road, keeping you safe. There are a couple of easy ways to do this.
A tread depth gauge is the most accurate way.
Tire tread depth gauges can be found online or at your local auto parts store, and they are easy to use. The best way to measure your tread depth is to stick the probe into the shallowest groove on the tire, press the shoulders of the probe flat against the tread and then read the result.
All gauges should measure both in the 1/32" United States standard and in millimeters.
If your gauge measurement reads:
6/32" or higher: Your tire’s tread depth is sufficient.
5/32": If snow-covered roads are a concern, you should consider replacing your tires.
4/32": If you frequently drive on wet roads, consider replacing your tires.
3/32": It’s time to start shopping for new tires. They are close to being worn out.
2/32" or lower: Your tires are legally bald, and it’s time to replace them.
If you don’t have a tread depth gauge handy, some U.S. coins can be used to approximate wear on tires in the critical last 32nds of an inch of their remaining tread depth. A penny or a quarter can work, depending on how conservative you want to be or if you frequently drive in rainy or snowy roads.
Here’s how it works:
Place a penny with Lincoln’s head upside down and facing you into the shallowest groove on the tire. If all of Lincoln's head is visible above the tread, you have only 2/32" or less tread depth left and your tire has reached the end of its useful life.
For those who drive in the rain or want an earlier warning that replacement time is coming, use a quarter. Place the quarter with Washington’s head upside down and facing you into the shallowest groove. If all of Washington's head is visible above the tread, you have 4/32" or less tread depth remaining.
If you’re into routine tread checks as much as we are and just want to see how well your tires are wearing, Lincoln can help here too. This time, place a penny with the Lincoln Memorial upside down and facing you. If the top of the Lincoln Memorial is visible above the tread, you have 6/32" or less tread depth remaining. It’s not time to panic, but it’s a good idea to continue to check your tread regularly.
Indicator bars also allow you to monitor tread wear. U.S. Federal safety standards require that tire tread patterns include 2/32" tread wear indicators across their tread, in the grooves. Tires are considered worn out when the tire’s tread pattern has worn even with the indicator bars.
Please note that, for those driving on winter tires, tread depth measurements follow a different set of replacement thresholds. Consult the manufacturer for recommended tread depth measurements and replacement schedules.
Tread depth is important. Tires at or above the recommended tread depth give you better traction in all types of driving conditions. Plus, checking your tread depth on a regular basis provides a good opportunity to inspect your tires for other signs of adverse wear or damage as well, such as cracks, bulges or cuts in the tread or sidewalls. If you’re ever concerned about your tires for any reason, it’s always a good idea to have them inspected by a professional.
Vehicles do not always come with a spare tire, but you might not notice this until it’s too late (when you are on the side of the road with a flat). It’s important to always have a back-up plan. Tireamerica.com has a guide created to help you understand the best options for you.