255/70R18 Tire Size
255/70R18 diameter, sidewall, revolutions per mile, and plus-sizing options.
The 255/70R18 tire size breaks down as: 255 mm section width, 70% aspect ratio, and a 18-inch rim. Below are its real, calculated dimensions.
255/70R18 Calculated Dimensions
| Metric | Value |
|---|---|
| Overall diameter | 32.1 in (814 mm) |
| Sidewall height | 7.0 in (179 mm) |
| Circumference | 100.7 in (2558 mm) |
| Revolutions per mile | 629 |
Typical Fitment
255/70R18 is most often found on full-size SUVs. Always confirm against the door-jamb placard or owner manual before fitting.
Plus-Sizing Alternatives
These sizes keep the overall diameter close to 255/70R18, so speedometer and gearing stay near stock:
| Size | Diameter | Diameter change |
|---|---|---|
| 265/65R18 | 31.56 in | -1.5% |
| 265/65R19 | 32.56 in | +1.6% |
| 275/55R20 | 31.91 in | -0.5% |
Speedometer Note
If you fit a 265/65R18 instead of 255/70R18, the diameter changes by -1.5%. A taller tire makes your speedometer read low — at a true 60 mph it would show roughly 61 mph. A shorter tire has the opposite effect, so the gauge reads high.
Use the tire calculator to compare 255/70R18 against any other size and see the exact diameter and speedometer difference.
Frequently Asked Questions
What does 255/70R18 mean?
255/70R18 means a 255 mm wide tire with a 70% 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 255/70R18?
Yes, as long as the replacement keeps the overall diameter close to stock so the speedometer stays accurate. Common plus-size moves from 255/70R18 are 265/65R18, 265/65R19, 275/55R20.
Will 255/70R18 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.