245/40R20 Tire Size
245/40R20 diameter, sidewall, revolutions per mile, and plus-sizing options.
The 245/40R20 tire size breaks down as: 245 mm section width, 40% aspect ratio, and a 20-inch rim. Below are its real, calculated dimensions.
245/40R20 Calculated Dimensions
| Metric | Value |
|---|---|
| Overall diameter | 27.7 in (704 mm) |
| Sidewall height | 3.9 in (98 mm) |
| Circumference | 87.1 in (2212 mm) |
| Revolutions per mile | 728 |
Typical Fitment
245/40R20 is most often found on luxury 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 245/40R20, so speedometer and gearing stay near stock:
| Size | Diameter | Diameter change |
|---|---|---|
| 255/40R20 | 28.03 in | +1.1% |
| 255/35R21 | 28.03 in | +1.1% |
| 265/25R22 | 27.22 in | -1.8% |
Speedometer Note
If you fit a 255/40R20 instead of 245/40R20, the diameter changes by +1.1%. 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 245/40R20 against any other size and see the exact diameter and speedometer difference.
Frequently Asked Questions
What does 245/40R20 mean?
245/40R20 means a 245 mm wide tire with a 40% 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 245/40R20?
Yes, as long as the replacement keeps the overall diameter close to stock so the speedometer stays accurate. Common plus-size moves from 245/40R20 are 255/40R20, 255/35R21, 265/25R22.
Will 245/40R20 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.