How to Measure Tire Tread Depth and Why It's Important

Video tutorial on how to measure the tread depth of a tire. Beyond visually inspecting a tire, the measurement of tread depth will help determine if the tires will pass a certification inspection, tires have incorrect pressure, there is fault with the suspension components, unbalanced tire, an alignment issue, worn steering or suspension components, and a fault with the tire. In order to maintain equal tread depth, it’s important to maintain your vehicle’s suspension and steering components. It is also extremely important to have your tires rotated, so if you do have a negative camber, when tires are switched to the other side, this helps promote an even wear. As a generalized recommendation, tires should be rotated every 12,000 km or 8,000 miles, but this may vary between manufacturers and drive systems. As a tolerance value between tire tread wear measurements, this can vary between manufactures and drive systems as well. From some manufacturer specifications, Audi states that the rolling radius of all four tires must be within 4/32 of an inch. The Porsche Cayenne must be within 30% of the opposite wheel on the same axle. And Subaru, must be within 1/4 inch of tire circumference or with 2/32 of an inch of each other. If these values exceed these limits, the can cause premature failure of drive components or faults with vehicle’s computers as each wheel would be turning at a different speed.

Tools/Supplies Needed:

• tire tread depth gauge
• vernier caliper

First inspecting the shoulder of the tire which is where the tread starts as the sidewall ends. Here we are looking for small arrow which indicates where the wear bars are located within the tire treads. Some may have text as well which maybe written in such a way to break the tire down into segments if you are recording the numbers.

Wear bars are a raised portion within the tread groves which indicates how much life is left in the tires. When the depth reaches a certain measurement, than the tires are becoming unsafe to use and will need to be replaced. Now the amount of wear bars across the tread face will also vary depending on the tire’s design.

Here I have a tire tread depth gauge which are only a few dollars to purchase and very easy to use. These are available in a variety of styles and can even be found in a digital version. If you don’t have one of these, I will show you an alternative method.

First extend the plunger all the way out.

Push the plunger down, not on the wear bar though, this measurement uses the total tread depth instead. The plunger will stop, be sure the outer stopper portion on the case is touching the tread face, remove and then take the reading. Tire tread depth gauges normally have both imperial and metric values.

First I will be working with an almost brand new tire.

The first measurement is 9/32 or 7mm. We are looking for which measurement line meets the casing of the depth gage.

The second measurement is the same.

And finally the third measurement, which is also the same.

As a second example, I will be using my winter tires.

So for this tire the first measurement is about 7/32 or 6mm

5/32 or 4mm is the next measurement.

And finally the third is the same and the middle measurement, 5/32 or 4mm. So these measurements would show that the vehicle has a negative camber which could be from an alignment issue, a lowered vehicle, or it could be the nature of the independent suspension depending on the design.

As an alternative method, you can use a caliper. Calipers are available in a variety of styles and if you are unsure how to use one, I have a tutorial on that which I will include in the description below. The caliper is equipped with a depth gauge, same type of idea as a tire depth gauge. This method is certainly much more accurate.

Extend the depth gauge out to an appropriate length, then insert in the groove.

Remove and record the measurement. Here we have 0.275”.

Next is 0.279”.

And the last is 0.285”.

Next I have a worn tire example and as you can see the wear bars are even with the thread face. Therefore the tire is in need of a replacement.

Tire tread depth ratings will vary between countries, so check your local government speculations.

In order to maintain equal tread depth, it’s important to maintain your vehicle’s suspension and steering components. It is also extremely important to have your tires rotated, so if you do have a negative camber, when tires are switched to the other side, this helps promote an even wear. As a generalized recommendation, tires should be rotated every 12,000 km or 8,000 miles, but this may vary between manufacturers and drive systems.

As a tolerance value between tire tread wear measurements, this can vary between manufactures and drive systems as well. From some manufacturer specifications, Audi states that the rolling radius of all four tires must be within 4/32 of an inch. The Porsche Cayenne must be within 30% of the opposite wheel on the same axle. And Subaru, must be within 1/4 inch of tire circumference or with 2/32 of an inch of each other. If these values exceed these limits, the can cause premature failure of drive components or faults with vehicle’s computers as each wheel would be turning at a different speed.

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