305/25R20 Tire Size
305/25R20 diameter, sidewall, revolutions per mile, and plus-sizing options.
The 305/25R20 tire size breaks down as: 305 mm section width, 25% aspect ratio, and a 20-inch rim. Below are its real, calculated dimensions.
305/25R20 Calculated Dimensions
| Metric | Value |
|---|---|
| Overall diameter | 26.0 in (660 mm) |
| Sidewall height | 3.0 in (76 mm) |
| Circumference | 81.7 in (2075 mm) |
| Revolutions per mile | 776 |
Typical Fitment
305/25R20 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 305/25R20, so speedometer and gearing stay near stock:
| Size | Diameter | Diameter change |
|---|---|---|
| 315/25R20 | 26.20 in | +0.8% |
| 315/20R21 | 25.96 in | -0.2% |
| 325/15R22 | 25.84 in | -0.6% |
Speedometer Note
If you fit a 315/25R20 instead of 305/25R20, the diameter changes by +0.8%. A taller tire makes your speedometer read low — at a true 60 mph it would show roughly 60 mph. A shorter tire has the opposite effect, so the gauge reads high.
Use the tire calculator to compare 305/25R20 against any other size and see the exact diameter and speedometer difference.
Frequently Asked Questions
What does 305/25R20 mean?
305/25R20 means a 305 mm wide tire with a 25% 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 305/25R20?
Yes, as long as the replacement keeps the overall diameter close to stock so the speedometer stays accurate. Common plus-size moves from 305/25R20 are 315/25R20, 315/20R21, 325/15R22.
Will 305/25R20 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.