How to read a tire size
Every tire has a size printed on the sidewall, for example 225/45R17. Each part of that code tells you something about the tire.
225/45R17
225
width (mm)
width (mm)
45
aspect ratio (%)
aspect ratio (%)
R
radial construction
radial construction
17
wheel diameter (in)
wheel diameter (in)
The parts, one by one
| Part | Meaning |
|---|---|
| 225 | Section width of the tire in millimeters, from sidewall to sidewall. |
| 45 | Aspect ratio: the sidewall height is 45% of the width. A lower number means a shorter, stiffer sidewall. |
| R | Radial construction, used on nearly all modern passenger tires. |
| 17 | Wheel diameter in inches. The tire must match the wheel. |
Load index and speed rating
After the size you may see a code like 94V. The number is the load index, the maximum weight one tire can carry. The letter is the speed rating. Use the codes printed on your tire or in your owner's manual, and never go below the manufacturer's specification.
Other numbers on the sidewall
DOT date code: the last four digits show when the tire was made. "2421" means week 24 of 2021. Tires age even when they are not driven, so check this on used tires.
Changing sizes? A different size can affect speedometer accuracy, ride, and clearance. Stay within the sizes your vehicle's manufacturer lists, or ask a tire professional before you change.
Call (442) 999-5014 about your tires
Reyes Tires Pro · 260 N Juniper St, Escondido, CA 92025