How to Measure Tire Tread Depth And Why It Matters

Shawn
| Last Updated: April 8, 2021

Tread depth is one of the more important safety checks that you can do on your vehicle. When accelerating, braking, or steering, you only have a small patch of rubber between your hundreds of pounds of motor vehicle and the hard surface of the road. 

If that small rubber patch isn’t in good condition, the risks you’re subjecting yourself and your passengers to are pushed higher than acceptable.

Here we’ll talk about that patch of rubber and how to make sure it’s legal.  

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Quick Questions Before Starting

Measuring the tread depth on your tires is a simple procedure that you can do on your own. It’s not a skilled task. It should be scheduled regularly, depending on how many miles you drive in a month.

How Difficult Is This to Do?

This is a straightforward task that needs no experience to undertake.

How Long Does it Take?

This should take you no longer than 30 minutes to check all four wheels and the spare.

How Much Do Materials Cost?

If you’re using a penny or a quarter to do a rough check, there’s no cost. If you want to measure the tread depth accurately, a tread depth gauge will have to be purchased. A good manual gauge will cost in the region of $5 to $12 and a digital gauge between $13 and $15.

Things You Can Use to Check Tire Tread

There are four ways that you can check the tread remaining on your tires. Only one of these methods requires you to buy a tire tread depth gauge. The others are household items or built into the tire. 

Tread Wear Indicator

On all tires, there’s a treadwear indicator built into the tread. If you look at the tread, you’ll see bands of rubber placed across the widest grooves of the tread at regular intervals around the tire's circumference. 

If you look at the tire's side, you’ll see the letters TWI meaning Tread Wear Indicator. If the tread of the tire is level with the indicators, it means that your tires must be replaced.

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Penny Test

A simple test that will give you a good idea of whether your tires are worn is to use a penny. Hold the penny with Lincoln's head facing toward you and with the head pointing down toward the surface of the tire. Drop the penny into the grooves of the tread. 

If you can see all of Lincoln's head, it means your tire must be replaced as the depth is less than ²/₃₂ ". If any of his head is obscured, your tire is good to go.

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Quarter Test

Another simple test with a coin is to use a quarter. Again, hold the quarter with Lincoln's head facing you and with the head pointing at the surface of the tire. Drop the quarter into the grooves of the tread. 

If the tread touches Lincoln's head, then you have approximately ⁴/₃₂" of tread left. This means the tire is still legal, but it’s getting very close to its legal limit, and you should be making plans to replace it.

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Tire Tread Gauge

The most accurate means of measuring tread depth is to use a tread depth gauge. These gauges can be purchased from any good auto parts store or online. All of them work similarly. At one end will be a pointer that you place in the groove of the tread. You then push the barrel of the gauge down until it touches the raised portion of the tread. 

Digital gauges have a screen where you can read the tread depth, but manual gauges need you to read the scale at the top of the gauge. A manual gauge should cost you between $5 and $12 and a digital gauge between $13 and $15. 

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How to Measure Tire Tread Depth: 4 Methods

It’s straightforward to measure the depth of tread left on your tires. This is a task that anyone can undertake, and you require no special training.

The first thing that you should do is look at the tread across the tire. If there’s any place where the tread is worn down more than anywhere else, then you must measure the most worn part of the tire. 

Uneven tread depth indicates a problem with your wheels' alignment and needs to be repaired as soon as possible. Remember to measure all the tires on the vehicle and don’t forget the spare.

If you drive on winter tires, certain SUV tires, high-performance tires, or truck tires, please refer to the manufacturer's specifications for the tread depth. These tests don’t apply to these types of tires.

1. Using the Tread Wear Indicators on the Tire

a. Sit comfortably by the tire so you can see the sidewall and the tread clearly.

b. Make sure the sidewall is clean so you can read the text on it.

c. Look for the letters TWI on the sidewall. These stand for Tire Wear Indicator.

d. From these letters, run your finger up to the tread of the tire.

e. Now carefully look at the tread. In the grooves between the tread blocks, you should see bars of rubber running across the grooves.

f. These bars are the minimum legal depth of tread for the tire.

g. If these bars are level with your tread, then the tire must be replaced.

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2. Penny Test

a. Sit comfortably next to the tire so that you can clearly see the tread.

b. Hold the penny with Lincoln's head facing toward you and with the head pointing down toward the surface of the tire. 

c. Drop the penny into the grooves of the tread until it can go no further.

d. If you can see all of Lincoln's head, it means your tire must be replaced as the depth is less than ²/₃₂ ". If any of his head is obscured, your tire is good to go.

Photo credit: nissanofmobile.com

3. Quarter Test

a. Sit comfortably next to the tire so that you can clearly see the tread.

b. Hold the quarter with Lincoln's head facing you and with the head pointing at the surface of the tire. 

c. Drop the quarter into the grooves of the tread until it can go no further.

d. If the height of the tread block touches Lincoln's head, then you have approximately ⁴/₃₂" of tread left. This means the tire is still legal, but it’s getting very close to its legal limit, and you should be making plans to replace it.

Photo credit: idrivesafely.com

4. Tire Tread Gauge

a. Sit comfortably next to the tire so that you can clearly see the tread.

b. Push the end of the gauge that has the scale on it so that the other end is sticking out of the gauge's barrel.

c. Place the gauge's pointed end into the groove of the tread, and gently push the barrel down until it rests on the tread blocks.

d. If you have a manual gauge:

     i. Slowly rotate the scale until you see the first number, where a line is clearly visible underneath it.

     ii. The scale is printed in measures of ¹/₃₂". This means that the number is the depth of your tread in multiples of ¹/₃₂". So if your gauge reads 5, then the tread depth is ⁵/₃₂" deep, and it’s still legal, but if it’s ²/₃₂", it’s illegal and dangerous. 

e. If you’re lucky enough to have a digital gauge, you simply read the depth measurement off the little screen.

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Why Tread Depth Matters 

As you drive, only a small patch of rubber is actually in contact with the road at only one time. This means that you must keep your tires in tip-top condition so that you always have quality rubber meeting the road, ensuring yourself and your passengers' safety. The depth of the tread that’s in contact with the road is important.

Like those fitted to high-end sports cars, high-performance tires have a short fat contact patch on the road, as they’re intended for speed. This fat patch gives stability when cornering and when traveling at speed. It also gives more traction as there’s more rubber pushing against the road surface.

The patch on the road is longer and thinner for the average family car, this gives a more comfortable ride. This type of patch is also quieter and better at wicking water away from the tire in wet weather. Also, a thinner surface patch gives less resistance. The car rolls forward better, using less fuel and providing a smoother ride.

This patch is responsible for adhering to the road and ensuring that water is safely removed from under the tire, so the car doesn’t slide or aquaplane on the water. This is why the tread on the tire is so essential. 

The grooves and tread blocks provide a safe ride and ensure that hazards such as water are safely removed. If the tread is very shallow or non-existent, these hazards reach dangerous levels.

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Conclusion 

Tires are one of the major safety components of your vehicle and, as such, should be treated with care. Driving on tires with uneven wear or illegal tread depth will expose you and your passengers to unnecessary risks. 

This risk is exacerbated in wet weather. When a vehicle hydroplanes, it’s uncontrollable and a serious accident will be the result. Don’t risk putting yourself at risk of killing or injuring someone else. Check your tread depth, and if it’s below the recommended level, change your tires.

People Also Ask

There are always many questions around tread depth, and your local tire dealer will be able to answer many of them, but here are some of the most common questions. 

What is the Minimum Tire Tread Depth That’s Safe?

In the USA, the minimum tread depth that’s considered safe on ordinary passenger car tires is ²/₃₂". For winter tires, certain SUV tires, high-performance tires, and truck tires, please refer to the manufacturer's recommendations for the correct tread depth.

Is the Penny Test for Tires Accurate?

Yes, the penny test is accurate, proving the penny is in good condition and hasn’t been damaged. However, this is a very rough test, and using a proper tread depth gauge is the most accurate means of measuring the depth.

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How Many 32nds Are on a New Tire?

The standard family vehicle tire comes with ¹º/₃₂" or ¹¹/₃₂" tread depths when new. These tread depths will be different for specialized tires such as winter tires, some SUV tires, mud terrain tires, and truck tires.

How Much Tread Does a New Tire Have?

A new tire will have the full depth of tread that applies to that type of tire. It varies between tires intended for different applications. If you’re in doubt, refer to the manufacturer's handbook or speak to your local tire dealer.

When Are Cracks in Tire Tread Unsafe?

If the cracks are lightly scoring the surface, they’re likely cosmetic, but if the crack extends 1.5 - 2 millimeters into the tread block, then the tire must be taken to a dealer to be checked. 

These cracks could indicate old age, where the rubber has perished, and the cracks expose the tire's internals to oil, water, and other contaminants that could cause further damage and make the tire unsafe.

Shawn

An ex-salesman of industrial equipment, Shawn used to drive nearly 60K miles a year just commuting to clients. He also has a little project Miata build going on the side. Safe to say, Shawn has slain a few tires in his days. He knows all about horrid road-noise, hydroplaning risks, and how much damage a bad alignment can do to your wallet. He enjoys helping us out and Chris always values his opinion when designing something new for the website.