Reading Your Tire Size
Every tire has a size code on its sidewall. Here's how to read it:
Example: 225/45R18 97W
Let's break this down:
225 — Width (mm)
The tire's width from sidewall to sidewall, in millimeters. A 225 tire is 225mm (about 8.9 inches) wide.
Common widths: 205, 215, 225, 235, 245, 255, 265, 275
45 — Aspect Ratio (%)
The sidewall height as a percentage of the width. A 45 aspect ratio means the sidewall is 45% of 225mm = ~101mm tall.
R — Construction
"R" means radial construction. Virtually all modern tires are radial.
18 — Wheel Diameter (inches)
This tire fits an 18-inch wheel. Must match your wheel size exactly.
97 — Load Index
The maximum weight each tire can support. 97 = 730 kg per tire. Your replacement tires should meet or exceed the original load index.
W — Speed Rating
The maximum safe speed. W = 270 km/h. For winter tires, the speed rating is often lower (T = 190 km/h, H = 210 km/h), which is perfectly fine for Canadian speed limits.
Where to Find Your Tire Size
Three places to check:
What If My Car Has Two Different Sizes?
Some vehicles (BMW, Mercedes, Porsche) have staggered fitment — wider tires on the rear than the front. For example:
This is normal for performance vehicles. You'll need to buy tires in pairs (2 front + 2 rear) instead of a set of 4.
Not Sure? Just Take a Photo
At TireGPT, you can upload a photo of your tire sidewall and our AI will read the size for you automatically. No squinting required.