345/30R20 Tire Size
345/30R20 diameter, sidewall, revolutions per mile, and plus-sizing options.
The 345/30R20 tire size breaks down as: 345 mm section width, 30% aspect ratio, and a 20-inch rim. Below are its real, calculated dimensions.
345/30R20 Calculated Dimensions
| Metric | Value |
|---|---|
| Overall diameter | 28.1 in (715 mm) |
| Sidewall height | 4.1 in (103 mm) |
| Circumference | 88.4 in (2246 mm) |
| Revolutions per mile | 716 |
Typical Fitment
345/30R20 is most often found on exotic performance cars. Always confirm against the door-jamb placard or owner manual before fitting.
Plus-Sizing Alternatives
These sizes keep the overall diameter close to 345/30R20, so speedometer and gearing stay near stock:
| Size | Diameter | Diameter change |
|---|---|---|
| 355/30R20 | 28.39 in | +0.8% |
| 355/25R21 | 27.99 in | -0.6% |
| 365/20R22 | 27.75 in | -1.4% |
Speedometer Note
If you fit a 355/30R20 instead of 345/30R20, the diameter changes by +0.8%. 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 345/30R20 against any other size and see the exact diameter and speedometer difference.
Frequently Asked Questions
What does 345/30R20 mean?
345/30R20 means a 345 mm wide tire with a 30% sidewall aspect ratio mounted on a 20-inch rim. The aspect ratio is the sidewall height as a percentage of the width.
Can I plus-size from 345/30R20?
Yes, as long as the replacement keeps the overall diameter close to stock so the speedometer stays accurate. Common plus-size moves from 345/30R20 are 355/30R20, 355/25R21, 365/20R22.
Will 345/30R20 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.