How to Read a Winter Tire's Sidewall: A Plain-English Guide for Calgary Drivers
How to Read a Winter Tire's Sidewall: A Plain-English Guide for Calgary Drivers
A winter tire's sidewall tells you almost everything you need to know before you buy — size, load capacity, speed rating, and whether the tire actually meets the standard for driving on snow and ice. The most important symbol to look for is the mountain-with-snowflake (called the Three-Peak Mountain Snowflake, or 3PMSF), which certifies the tire passed an independent winter traction test. Everything else — load index, speed rating, DOT date code — confirms the tire is the right fit for your vehicle and hasn't aged past the point where you'd trust it on Deerfoot in a February snowstorm.
The short version
- The size code (e.g., 225/65R17) gives you width in mm, sidewall ratio, and rim diameter in inches
- Load index and speed rating confirm the tire handles your vehicle's weight and rated speed
- The 3PMSF snowflake = independently tested for winter; M+S alone is not enough for a Calgary winter
- The DOT code contains the manufacture date — tires over six years old deserve a closer look
- UTQG grades don't apply to winter tires, so ignore them when shopping for snow rubber
- When in doubt, bring your door jamb sticker and we'll do the matching for you
The size code: what 225/65R17 actually means
That string of numbers and letters stamped on the sidewall is the tire's size designation. Breaking down 225/65R17 as a typical example:
- 225 — section width in millimetres, measured sidewall to sidewall when mounted on the correct rim width
- 65 — aspect ratio: the sidewall height is 65% of the section width, about 146 mm tall
- R — radial construction, standard on every modern passenger tire
- 17 — rim diameter in inches; this must match your wheel exactly
You may see a prefix before the number. P stands for Passenger, meaning the tire uses North American load-rating standards for passenger vehicles. LT stands for Light Truck and signals a different, typically higher load capacity and thicker sidewalls. Your door jamb sticker shows the exact size your vehicle needs — check it before you shop.
If you want to go deeper on decoding tire sizes, our post on how to read a tire size walks through it with more examples.
Load index and speed rating
Right after the size designation you'll see something like 91T or 103H. The number is the load index — a coded value representing the maximum weight each individual tire can safely carry. Load index 91 works out to 615 kg per tire; load index 103 is 875 kg. You can exceed the minimum your vehicle requires, but never go below it.
The letter is the speed rating: T is rated to 190 km/h, H to 210 km/h, V to 240 km/h. Alberta highways cap at 110 km/h, so even a T-rated winter tire won't hold you back on your daily commute. What matters is consistency — ideally all four tires share the same speed rating. Mixing significantly different ratings, especially front-to-rear, can affect braking balance on ice.
The symbols that actually matter in a Calgary winter
There are two symbols you'll see on tires marketed for winter or all-season use, and the difference between them is significant:
- M+S (Mud and Snow) — a self-certified designation. Manufacturers apply it to their own tires without any independent test required. Many all-season tires carry M+S. That alone does not make them a winter tire.
- 3PMSF (Three-Peak Mountain Snowflake) — a tire must pass a standardized snow traction test showing at least 10% better grip than a reference all-season tire on packed snow. This is the minimum standard for genuine winter performance.
Calgary winters are unpredictable — ice on Deerfoot one morning, a chinook melting everything by afternoon, then back to packed snow two days later. A tire certified only for mud and light snow won't hold when the temperature drops and stays there. Look for the 3PMSF snowflake before you buy.
Our winter tires Calgary page covers the key differences between tire categories in more detail. And if you're planning ahead, our seasonal tire changeover page explains what the swap process looks like from drop-off to pickup.
The DOT code: reading a tire's age
Every tire sold in North America carries a DOT code — a stamped string starting with "DOT" that ends with a four-digit week-year number. For example, 3824 at the end of the DOT string means the tire was manufactured in week 38 of 2024 — late September 2024.
Rubber compounds degrade over time, including tires sitting untouched in a garage that look perfectly fine from the outside. General guidance on tire age:
- Under 6 years from manufacture — good to go
- 6–10 years — have a technician inspect for sidewall cracking and compound hardening before continuing to use
- Over 10 years — replace regardless of remaining tread depth
If you're buying used winter tires, always check the DOT stamp before you hand over any money. A cheap set dated 2015 is not a deal. Older tires also frequently have dead TPMS sensors — if you end up with a warning light after a changeover, our TPMS service page explains what's involved, and our post on what the TPMS warning light means covers the details.
UTQG grades: useful for summer shopping, not for winter
Some tire sidewalls display a three-part rating like 500 AA A. This is the Uniform Tire Quality Grade (UTQG): treadwear, traction, and temperature resistance. Higher treadwear numbers generally mean longer-lasting rubber; traction grades run from C up to AA.
Here's what most buyers don't know: UTQG grades are not required on winter tires, and most winter tires don't carry them. The UTQG traction test measures stopping distance on wet pavement — not ice or packed snow. Winter tires are engineered around cold-weather grip, which shows up in the 3PMSF certification, not the UTQG traction score. If you don't see UTQG grades on a winter tire's sidewall, that's completely normal.
When to stop reading and just ask
There's no shame in walking in with your door jamb sticker and handing it over. At Prince Tires, we've been matching Calgary drivers to the right winter tires since 2021. We'll tell you exactly what the sidewall specs mean for your vehicle, which sizes we have in stock, and whether same-day service is available when you book ahead. We're family-owned, open seven days a week, and all our tire installations come with warranties included.
The changeover window in Calgary is short. Book before October is out — ideally when overnight lows are consistently at or below 7°C. Once the first big snowfall hits, every shop in the city fills up fast. Our post on when to change to winter tires in Calgary has the timing breakdown if you want specifics.
Frequently asked questions
What's the difference between the 3PMSF snowflake symbol and M+S?
M+S is a self-certified label — manufacturers apply it themselves with no independent test required. The Three-Peak Mountain Snowflake requires passing a standardized test showing at least 10% better traction on packed snow than a reference all-season tire. For Calgary winters, M+S on its own is not enough. Look for the snowflake.
Do I need to exactly match the load index from my original tires?
Never go below the minimum load index your vehicle requires — that number is a safety floor set by the manufacturer. Going above it is fine; a load index of 95 where 91 is required just means the tire can carry more than needed. Your door jamb sticker has the minimum, and we'll confirm it when you book in.
My winter tires have a "P" at the start of the size — does that matter?
P-metric and LT (Light Truck) tires use different load-rating systems. If your vehicle calls for P-metric, that's what you want. Trucks and larger SUVs may spec LT tires, which carry higher load ratings and thicker sidewalls. Mixing P and LT tires on the same vehicle can affect handling balance and isn't recommended.
How do I find the manufacture date on my tires?
Look for the four-digit week-year stamp at the end of the DOT code, usually on the inner sidewall. "3824" means week 38 of 2024 — late September 2024. If you're buying used tires, this check is non-negotiable. A tire can look perfectly fine while being well past a safe service life.
Can I run winter tires with different speed ratings on the same vehicle?
You can, but the set's effective speed limit drops to the lowest-rated tire — and mixing ratings front-to-rear can affect braking balance on ice and packed snow. The safest approach is to match all four winter tires to the same speed rating. Never exceed the lowest-rated tire's maximum, regardless of posted speed limits.
Ready to get the right winter tires for your vehicle? Prince Tires is at 111 42 Ave SW, Calgary — open seven days a week. Our 4.9-star team (560+ Google reviews) offers same-day service when you book ahead, backed by our Price Match Guarantee. Call us at (403) 452-4283 or book your appointment online. Don't wait for the first snowfall.
Posted by the Prince Tires team. Last updated: August 2026.
