How to read a tire sidewall (2023)

Decoding your car's tire information doesn't require flipping through the owner's manual. All the information you need is right there on the sidewall. You just have to know how to crack the code. Not only do the jumble of letters and numbers tell you the size of the tire, but they can also tell you how safe your tires are and how old they are, too.

Let's take a look at the tires on Roadshow's long-term 2018 Kia Stinger for example.

The biggest stamping on the tire is the brand and model, in this case Michelin Pilot Sport 4. On this particular tire, there is also a note of "outside." This indicates that the tires are asymmetric and have a change of tread pattern across the tire that can disperse water while also maintaining dry grip.

Size matters

You might be confused by the following string of letters and numbers: "255/35 ZR19 (96Y)." That looks like someone's email password, doesn't it? 255/35 indicates that the tire is 255 millimeters wide, with a 35-percent sidewall aspect ratio. In other words, the height of the sidewall is 35 percent of the tread width.

Yes, tires make you do math.

Multiply 255 by 0.35 to get an 89.25 millimeter sidewall height. If you want to convert either of those numbers to inches, divide by 25.4, the number of millimeters in an inch. These tires are 10 inches wide and have a sidewall height of 3.5 inches.

(Video) How to Read a Tire Size & Understanding a Tire Sidewall

The "Z" indicates a speed rating of over 149 mph. There's more to it, however, and I'll explain the rest a bit further on.

"R" tells us that the tire has a radial construction. Radials are by far the most common type of passenger-car or truck tire, where the plies are situated perpendicular to the direction of travel.

In rare cases, perhaps if you drive a classic car on vintage-spec tires, you may see a "D" here, which indicates a diagonal or bias-ply construction. In these tires, the plies overlap each other on a diagonal.

How to read a tire sidewall (1)

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(Video) TIRES 101 | How to Read Tire Sidewall

You may also see the designation "F" after the construction-type symbol. This means the tire is a run flat and can be driven at slower speeds for a short distance after a puncture -- even after a complete loss of air pressure. Typically, the guideline in such scenarios is 50 mph for 50 miles.

"19" simply means the tire should be mounted on a wheel with a rim diameter of 19 inches. Luckily, no math is needed here.

On some tires you may see the note "M+S," which means the tire has been rated for mud and snow. You may also see a three-peak mountain graphic with a snowflake, indicating the tire is a step above an M+S tire for foul-weather performance.

It's important to note that neither of these symbols means the tire is specifically designed for mud or snow, just that it's been engineered to handle greater amounts of the slippery stuff than tires that don't have these markings. If you plan on driving in the deep snow or mud, you should consider a more specialized winter or off-road tire, respectively.

Locked and loaded

After the tire's size, you'll see its service description, here indicated by "(96Y)". The number is the load index. The higher the number, the more weight the tires can handle. In this case, "96" means the tire can handle 1,565 pounds, while the "Y" indicates the tire is rated to be safe at speeds up to 186 miles per hour.

But what about that "Z" rating mentioned earlier? "Z" means that the tire has been tested over 149 mph, but doesn't indicate how far over. The "Y" rating basically puts the cap at 186 mph. Except here, the designation is in parentheses, indicating that the tire has been tested above 186 mph. However, again it doesn't indicate how far over 186 mph that testing was done.

These speed ratings might matter to folks who take their Lamborghini Huracán to the track and have the capability of going over 186 mph, but for most of the driving public, a Y-rated tire, parentheses or no, should be more than sufficient for all street use.

(Video) The Ultimate Guide To Tire Sidewalls - How Good Are Your Tires?

If you'd like to see what the ratings are for your particular tire, Tire Rack has a few excellent chartshere.

Born-on date

The Department of Transportation leaves its mark on tires as well. On the sidewall, you'll find DOT followed by a series of numbers that indicate such things as manufacturing location and specs. However, the most important numbers are the last four, indicating the week and year the tire was made. In this case "1417" means it was made between April 3-9, 2017.

How to read a tire sidewall (2)

This information can be useful when assessing whether tires need to be replaced (which can be particularly helpful when shopping used cars). If the tires are over five years old, regardless of tread depth, it's time to get them inspected, and most likely replaced.

This born-on dating can also be helpful when attempting to figure out if your tires are affected by a recall.

Wear and tear

The Uniform Tire Quality Grade Standards are also molded on the tires, indicating treadwear, traction and temperature tolerances. While the tests to determine these criteria rely on standards set by both the DOT and National Highway Traffic Safety Administration, the testing itself is performed by the manufacturer, or an outside company it hires.

Treadwear testing is done on a controlled test track over 7,200 miles, and the resulting rating is comparative in relation to the test tire. A treadwear rating of 100 means the test subject is estimated to last as long as the test tire. Ergo, a tire rated at 200 promises to last twice as long as the test tire, but wear out twice as quickly as a tire rated at 400.

How to read a tire sidewall (3)

(Video) How to Read a Tire Sidewall

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Frankly, UTQGS isn't always the best way to determine probable wear, as the test tire runs through so few miles and wear will vary based on driving style and real-world conditions. Tire manufacturers' treadlife warranties are often a more useful indicator of projected life.

Traction rating designates a tire's wet stopping ability. The Michelins get the highest rating of AA, but you might see A, B or C here.

The temperature rating grades the tire on its ability to resist heat. A tire that can't dissipate heat will not be able to run safely at high speeds. The law requires a minimum grade of C, but the Michelins fitted on this particular Stinger go to the top of the class with an A grade.

To the max

Maximum load and tire pressure information must be marked on every tire sold in the United States. On these tires, we see noted "Max Load 710 kg" (1565 lbs) and "Max Press 340 kPa" (50 psi). This is not the same thing as the recommended tire pressure. For that information you should refer to the owner's manual or the information sticker on the driver's side door jamb.

You may also see an "E" with a number in a circle followed by some numbers. This means the tires meet European specifications, which vary slightly from US standards. Other codes include NOM for Mexico, CCC for China, SNI for Indonesia and N superimposed over an I for Brazil.

There is a lot to learn from the seemingly random assortment of numbers and letters on your tire's sidewall. Now that you know how to crack the code, you'll be able to take better care of your tires, or figure out when it's time to invest in new ones.

(Video) How to Read a Tires Sidewall

Originally published July 2018.


What do the markings on the sidewall of a tire mean? ›

See those markings on the tire sidewall? They are shorthand for a veritable wealth of information. The tire model name is present and correct, obviously, but that's just the start. There's also a sequence of numbers detailing the load index, speed rating, tire size, construction, and much more besides.

What number is the side wall of a tire? ›

This is the height of the sidewall from wheel to tread relative to the width. Manufacturer's represent this measurement in a percentage, so in our example, the sidewall is 129.25 millimeters — 5.08 inches — tall (235 x 0.55). The final number group, the “18,” is the size of wheel the tire fits.

Does it matter which side of a tire faces out? ›

The special tread cannot work properly if directional tyres are mounted the wrong way round. This means that the tyres will not hold the road very well and the risk of aquaplaning will be greater. Incorrectly mounted tyres will also wear down faster and they will be louder when driving.

How do I read tire codes? ›

The last four numbers represent the manufacturer's date. The first two numbers indicate the week, while the last two indicate the year. (For example, a tire with the number 2910 was manufactured in the 29th week of 2010.)

What does 225 50 r17 mean? ›

What 225/50R17 Means. The number 225 identifies the tire section width (the measurement of the tire from sidewall to sidewall in millimeters). This tire has an aspect ratio of 50 means that the tire's section height is 50% of the tire's section width.

What does 265 70 r17 mean? ›

265 is the width, 70 is the aspect ratio, R stands for radial, 17 is the wheel diameter and 115T is the load index and speed symbol. Cookie Settings.

What happens if you put directional tires on the wrong way? ›

On directional tires, there's an arrow on the sidewall of the tires — when correctly mounted, the arrow points toward the front of the vehicle. If directional tires get mounted backward, you won't get the hydroplaning resistance and other performance driving benefits the tread is designed for.

Is there an inside and outside to a tire? ›

If you have directional tires on your vehicle, they are simply marked by an arrow, and most of the time the word rotation, or direction of rotation, etc. Asymmetrical tires have an inside and outside to their tread. Tire manufactures will often do this to optimize the traction and wear capabilities of the tire.

What can happen if a tire is put on backwards? ›

What Happens If You Put Tires On Backwards? It depends on the situation. If you are driving in dry conditions on the road, then you probably wouldn't even notice that you are driving on backward directional tires. The tires may have a little bit of extra wear on them, but the car will be completely fine to drive.

What does 265 65R17 112S mean? ›

To sum up, a 265/65R17 112S tyre has a tread width of 265 millimetres, a profile of 65 and is a radial tyre that fits on a 17-inch rim. The load index (112) indicates a maximum load capacity of 1120kg and a S speed rating certifies it up to 180kph.

What do the symbols on tires mean? ›

There are two common grading systems for tires to help identify winter tire traction capabilities. All tires that pass certain winter tire traction tests can be marked with a symbol molded onto the side of the tire. One is the M+S (mud and snow) symbol, and the second is the mountain/snowflake symbol.


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