How to Read Tire Size: Numbers, Letters and Fitment
Your tire size is printed on the sidewall, but the vehicle’s tire information label and owner’s manual are the starting point for choosing replacements. Copy the complete specification—not just the wheel diameter—before you shop.
Where to Find Your Tire Size
Open the driver’s door and look for the tire and loading information label. Check the owner’s manual, too. Compare those requirements with the tires currently installed; previous owners may have changed the wheels or fitted a different size.
Some vehicles use different front and rear sizes. Record both, along with the year, make, model and trim. If your vehicle has aftermarket wheels or suspension changes, have a qualified tire professional confirm the appropriate specification. NHTSA’s TireWise guide explains why vehicle requirements matter.
What Does 225/45R17 Mean?
- 225
- Nominal tire width
225 millimeters - 45
- Sidewall height ratio
45% of the width - R
- Construction type
Radial - 17
- Wheel diameter
17 inches
The “45” is a percentage, not a measurement in millimeters. The “17” identifies the wheel diameter, not the tire’s outside diameter. Changing any part of this code changes the specification; a nearby size is not automatically interchangeable. See Bridgestone’s tire-size explanation.
Read Beyond the Three Numbers
A complete marking may also include a load index, speed symbol and load designation. Two tires with the same dimensions can have different capabilities. Compare the full listing with your vehicle’s requirements.
Swipe sideways to see every column
| Marking | What to look for |
|---|---|
| Load index | A numerical code for carrying capacity. Confirm the required capacity for your vehicle. |
| Speed symbol | A tested speed capability. It is not a recommended driving speed. |
| XL or load range | A load-related designation to include in your comparison. |
| P, LT, ST or T | Keep the prefix: passenger, light truck, special trailer or temporary spare. These are not interchangeable labels. |
Ask your installer about run-flat or vehicle-specific requirements as well. Bridgestone’s sidewall guide covers load and speed information in more detail.
A Simple Tire-Size Shopping Checklist
- Take two clear photos. Capture the vehicle label and the complete sidewall marking. Photograph front and rear tires if their sizes differ.
- Start a size search. Use our tire finder, retaining any prefix when entering the full size.
- Open the product page. Compare the model, complete specification and intended use. A search match alone does not confirm compatibility.
- Check the package. Confirm whether the price covers one tire or a set, then review your cart quantity.
Send those photos and your vehicle details to our support team if something does not match. Mention modifications before ordering.
Tire Size FAQs
Does R17 mean the tire fits every 17-inch wheel?
No. Wheel diameter is only one requirement. Wheel width, load capacity, clearance and the vehicle’s approved specification also need checking.
Can I use a different tire size?
Only after the vehicle manufacturer or a qualified tire professional confirms an appropriate alternative. Do not choose a substitute from similar numbers alone.
Is the pressure on the sidewall the pressure I should use?
Use the vehicle label or owner’s manual for recommended inflation pressure. The sidewall maximum is a different value; see our monthly tire care checklist.
Browse all tires, choose the right seasonal category, and use our online buying checklist before checkout.
Ready for your next set?
Find your size, compare your options and ask us if you need a hand.