225/45R18 Tire Size
225/45R18 diameter, sidewall, revolutions per mile, and plus-sizing options.
The 225/45R18 tire size breaks down as: 225 mm section width, 45% aspect ratio, and a 18-inch rim. Below are its real, calculated dimensions.
225/45R18 Calculated Dimensions
| Metric | Value |
|---|---|
| Overall diameter | 26.0 in (660 mm) |
| Sidewall height | 4.0 in (101 mm) |
| Circumference | 81.6 in (2073 mm) |
| Revolutions per mile | 777 |
Typical Fitment
225/45R18 is most often found on sport sedans. Always confirm against the door-jamb placard or owner manual before fitting.
Plus-Sizing Alternatives
These sizes keep the overall diameter close to 225/45R18, so speedometer and gearing stay near stock:
| Size | Diameter | Diameter change |
|---|---|---|
| 235/45R18 | 26.33 in | +1.4% |
| 235/40R19 | 26.40 in | +1.7% |
| 245/30R20 | 25.79 in | -0.7% |
Speedometer Note
If you fit a 235/45R18 instead of 225/45R18, the diameter changes by +1.4%. A taller tire makes your speedometer read low — at a true 60 mph it would show roughly 59 mph. A shorter tire has the opposite effect, so the gauge reads high.
Use the tire calculator to compare 225/45R18 against any other size and see the exact diameter and speedometer difference.
Frequently Asked Questions
What does 225/45R18 mean?
225/45R18 means a 225 mm wide tire with a 45% sidewall aspect ratio mounted on a 18-inch rim. The aspect ratio is the sidewall height as a percentage of the width.
Can I plus-size from 225/45R18?
Yes, as long as the replacement keeps the overall diameter close to stock so the speedometer stays accurate. Common plus-size moves from 225/45R18 are 235/45R18, 235/40R19, 245/30R20.
Will 225/45R18 affect my speedometer?
Only if it differs in diameter from your original size. A taller tire reads low; a shorter tire reads high. Compare the two sizes with the calculator to find the percentage.