A car tire’s sidewall is stamped with several codes — not just random numbers, but important information about the tire’s size, construction, load capacity, and top speed rating. Understanding what they mean helps you choose a tire that’s correct, safe, and suited to how you drive.
Example: 225/45 R17 94W
Here’s what each part of the code means:
| Code | Meaning | Description |
|---|---|---|
| 225 | Tire Width | The first 3 digits — the tire's tread width, in millimeters. |
| 45 | Aspect Ratio | The next 2 digits — sidewall height as a percentage of width (taller sidewall = softer ride, lower sidewall = sportier handling). |
| R | Construction | R = Radial, the standard construction for passenger cars. |
| 17 | Rim Diameter | The wheel diameter this tire fits, in inches. |
| 94 | Load Index | A reference number for the max weight a single tire can carry (94 ≈ 670 kg). |
| W | Speed Rating | A letter for the tire's maximum safe speed (W ≈ 270 km/h). |
Why does getting the size right matter?
Fitting the wrong tire size can affect:
- Speedometer accuracy — a different overall diameter throws off the speedometer reading.
- Ground clearance — a tire that’s too large or too small can rub against the fender or suspension.
- Handling and grip — width and construction directly affect how the car grips the road.
Before replacing your tires, always check the size stamped on the sidewall, or use a size calculator to compare a new size against your current one before deciding.