How to Read a Tire Sidewall – Everything Those Numbers and Letters Actually Mean

Pick up any tire and look at the sidewall. It looks like a random string of numbers, letters, and symbols stamped into the rubber. Most drivers ignore it completely. That’s a mistake – because every single character on that sidewall tells you something specific and useful about the tire you’re buying, running, or replacing. Once you know how to read it, you’ll never look at a tire the same way again.

Here’s exactly what it all means.

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The Main Code – What That String of Numbers Actually Says

The most prominent marking on any tire sidewall looks something like this:

225/55R17 97H

This is the tire’s size and performance code. Every part of it means something specific.

225 – Tire Width

The first number is the width of the tire in millimetres, measured from sidewall to sidewall at the widest point. In this example, the tire is 225mm wide. A wider tire has a larger contact patch with the road – more grip in dry conditions but more vulnerability to hydroplaning in wet ones.

55 – Aspect Ratio

The second number is the aspect ratio – the height of the sidewall expressed as a percentage of the tire’s width. A ratio of 55 means the sidewall height is 55% of 225mm, which works out to about 124mm. Lower aspect ratios mean shorter sidewalls, which typically means sharper handling but a harsher ride. Higher ratios mean taller sidewalls and more cushioning over rough roads.

This is why low-profile tires look the way they do – they have a very low aspect ratio, sometimes as low as 25 or 30, which gives that stretched-over-the-rim appearance that performance vehicles favour.

R – Construction Type

The letter between the two sets of numbers indicates how the tire is constructed internally. R stands for radial, which is the construction method used on virtually every passenger vehicle tire made today. You may occasionally see B for bias-ply or D for diagonal – these appear on older vehicles, trailers, and some off-road applications.

17 – Rim Diameter

This number tells you the diameter of the wheel the tire is designed to fit, measured in inches. A tire marked 17 fits a 17-inch rim. Get this wrong and the tire simply won’t mount – it’s one of the most basic fitment checks when buying any tire. If you’re not sure what size rim you have, the team at Good Tire can check it instantly. Come in any day – no appointment needed at our Calgary location.

97 – Load Index

The load index is a number that corresponds to the maximum weight each tire can support when properly inflated. 97 translates to 730kg per tire – meaning the set can support a total of 2,920kg. Going below your vehicle’s required load index is dangerous and in some cases illegal. Always match or exceed the load index specified in your owner’s manual.

Here’s a quick reference for common load index values:

Load Index	Max Load Per Tire
85	515 kg
91	615 kg
95	690 kg
97	730 kg
100	800 kg
104	900 kg
108	1,000 kg
112	1,120 kg

H – Speed Rating

The letter at the end is the speed rating – the maximum sustained speed the tire is designed to handle safely. Common ratings you’ll see on Calgary roads:

Speed Rating	Max Speed
S	180 km/h
T	190 km/h
H	210 km/h
V	240 km/h
W	270 km/h
Y	300 km/h

H-rated tires are the most common on passenger vehicles. Never fit a tire with a lower speed rating than your vehicle’s top speed capability – even if you never intend to drive that fast. The rating also reflects the tire’s overall construction quality and heat tolerance.

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The DOT Code – The Most Important Number Most Drivers Never Check

After the size code, the most important marking on any tire sidewall is the DOT code. It looks something like this:

DOT MA L9 ABCD 2318

The only part most drivers ever need to focus on is the last four digits – in this case 2318. This is the manufacture date code.

• The first two digits are the week of manufacture – week 23
• The last two digits are the year – 2018

So a tire stamped 2318 was manufactured in the 23rd week of 2018.

Why does this matter? Rubber degrades from the inside out regardless of how a tire looks on the surface. Most tire manufacturers and safety organizations recommend replacing tires that are six years old or older – regardless of remaining tread depth. A tire that looks brand new but was made eight years ago has compromised rubber compounds that increase blowout risk.

This is especially important when buying used tires. At Good Tire, every used tire on our shelf has the DOT date checked as part of our 5-point inspection – we won’t sell you a tire that’s past its safe service life. That’s a standard not every used tire seller holds themselves to.

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M+S and the Snowflake Symbol – Not the Same Thing

Look for these two markings on any tire claiming winter capability:

M+S (Mud and Snow) – This marking means the tire meets a basic tread pattern requirement for mud and snow traction. It sounds reassuring but the standard is low – many all-season tires carry this marking without delivering meaningful winter performance.

Three-Peak Mountain Snowflake (3PMSF) – This symbol – a snowflake inside a mountain outline – is the real indicator of genuine winter capability. Tires carrying this symbol have been tested and confirmed to meet specific snow traction performance standards. If you’re driving Calgary winters, this is the symbol you want on your winter tires.

The difference matters more than most drivers realise. An M+S all-season tire and a 3PMSF-rated winter tire perform very differently below -10°C – a temperature Calgary hits regularly from November through February.

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UTQG Ratings – Treadwear, Traction, and Temperature

UTQG stands for Uniform Tire Quality Grading. It’s a US Department of Transportation rating system that appears on most passenger tires as three separate grades. You’ll see it printed as something like:

Treadwear 500 Traction A Temperature B

Treadwear

A comparative rating of expected tread life relative to a reference tire rated at 100. A treadwear rating of 500 means the tire should last roughly five times longer than the reference tire under controlled test conditions. Higher numbers generally mean longer tread life – but real-world results depend heavily on driving style, road conditions, and maintenance habits.

Common treadwear ratings by tire type:

• Performance summer tires: 200 to 400
• All-season tires: 400 to 700
• Touring tires: 600 to 800+

Traction

Rated AA, A, B, or C – measures wet braking performance on a straight line. AA is the highest rating. Most quality all-season tires score A or higher. Avoid tires rated C for any vehicle driven in wet conditions.

Temperature

Rated A, B, or C – measures the tire’s ability to dissipate heat at sustained speeds. A is the highest. All tires sold for highway use in Canada must meet at least a C rating. Look for A or B on any tire you plan to use at highway speeds regularly.

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Sidewall Markings You Might Also See

A few other markings worth knowing:

MAX INFLATE TO XX PSI – This is the maximum cold inflation pressure – not the recommended pressure for your vehicle. Your recommended pressure is on the sticker inside your driver’s door jamb. Never inflate to the sidewall maximum for normal driving.

OUTSIDE / INSIDE – Appears on asymmetric tires that must be mounted in a specific orientation. Install these backwards and the tire won’t perform as designed and will wear incorrectly.

ROTATION ARROW – Appears on directional tires that must rotate in a specific direction. These tires can only be rotated front to back on the same side of the vehicle – not across.

REINFORCED or XL (Extra Load) – Indicates the tire is built to carry higher loads than a standard tire of the same size. Common on SUVs and vehicles that regularly carry heavy loads or tow.

RFT or Run Flat – The tire is built with reinforced sidewalls that allow limited driving after a puncture – typically 80km at 80km/h. If your vehicle came equipped with run-flat tires, Good Tire can help with run-flat tire service and replacement when you need it.

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How to Use This Information When Buying Tires

Now that you can read a tire sidewall, here’s how to put it to work:

Step 1 – Find your current tire’s size code. It’s on the sidewall of any tire currently on your vehicle. Write it down exactly.

Step 2 – Check the DOT date on your current tires. If any are approaching or past six years old, budget for replacement regardless of how the tread looks.

Step 3 – Look for the 3PMSF snowflake on any tire claiming winter performance. M+S alone is not enough for Calgary winters.

Step 4 – Match or exceed your vehicle’s required load index and speed rating when replacing tires. Your owner’s manual lists the minimum specification.

Step 5 – When in doubt, ask. The team at Good Tire will look up the correct specification for your vehicle instantly and walk you through every option at every price point.

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Ready to Find the Right Tire for Your Vehicle?

Now that you know what every number and letter means, choosing the right tire is a much simpler conversation. Browse our full range of tires and wheel services in Calgary or check out our current tire brands to see what’s available for your vehicle.

Got a specific size in mind? Check our store specials – discounts of up to $100 are available on select brands right now.

📞 (403) 453-2008 📍 2125 52 St SE, Calgary – Open 7 Days, 9 AM to 7 PM No appointment needed – walk in any day and we’ll find the right tire for your vehicle.