33.1" tall, 10.0" wide, 7.5" sidewall
A 255/75R18 tire is 33.1 inches (840 mm) tall and 10.0 inches wide. The sidewall is 75% of the width, 7.5 inches, on a 18-inch wheel, and the tire turns about 610 times per mile.
In flotation terms that is about 33.1x10.0R18, closest to the common 33x12.50R18 (33.0"). People often call it a 33-inch tire.
The size most often compared with it is 275/70R18, which is 0.1" taller (+0.3%). At an indicated 60 mph you would be doing 60.2 mph on it.
| Current | New | Difference |
|---|
| Shows | Actual speed |
|---|
Same 18" wheel, within 20 mm of width and 10 points of aspect ratio.
| Size | Diameter | Width | Sidewall | vs 255/75R18 | |
|---|---|---|---|---|---|
| 275/70R18 | 33.2" | 10.8" | 7.6" | +0.3% | |
| 235/80R18 | 32.8" | 9.3" | 7.4" | −0.8% | |
| 265/70R18 | 32.6" | 10.4" | 7.3" | −1.4% | |
| 245/75R18 | 32.5" | 9.6" | 7.2" | −1.8% | |
| 265/75R18 | 33.6" | 10.4" | 7.8" | +1.8% | |
| 275/65R18 | 32.1" | 10.8" | 7.0" | −3.0% | |
| 255/70R18 | 32.1" | 10.0" | 7.0" | −3.0% | |
| 255/80R18 | 34.1" | 10.0" | 8.0" | +3.0% | |
| 235/75R18 | 31.9" | 9.3" | 6.9" | −3.6% | |
| 275/75R18 | 34.2" | 10.8" | 8.1" | +3.6% |
Sizes within 2% of 33.1" on 17" or 19" or 16" or 20" wheels.
| Size | Diameter | Width | Sidewall | vs 255/75R18 | |
|---|---|---|---|---|---|
| 255/80R17 | 33.1" | 10.0" | 8.0" | +0.0% | |
| 255/70R19 | 33.1" | 10.0" | 7.0" | −0.0% | |
| 255/85R16 | 33.1" | 10.0" | 8.5" | +0.0% | |
| 255/65R20 | 33.1" | 10.0" | 6.5" | −0.0% | |
| 33x12.50R16 | 33.0" | 12.5" | 8.5" | −0.2% | |
| 33x12.50R17 | 33.0" | 12.5" | 8.0" | −0.2% |
Actual speed when the speedometer is calibrated for 255/75R18.
| Speedometer shows | on 275/70R18 | on 235/80R18 | on 265/70R18 |
|---|---|---|---|
| 30 mph | 30.1 mph | 29.8 mph | 29.6 mph |
| 45 mph | 45.1 mph | 44.7 mph | 44.4 mph |
| 60 mph | 60.2 mph | 59.5 mph | 59.2 mph |
| 70 mph | 70.2 mph | 69.5 mph | 69.0 mph |
33.1 inches (840 mm). The sidewall is 7.5 inches.
10.0 inches (255 mm) section width, measured sidewall to sidewall.
About 33.1x10.0R18; the closest common flotation size is 33x12.50R18 at 33.0".
275/70R18 is +0.3% in diameter, within the common 3% guideline. It is 0.8" wider.