32.8" tall, 9.3" wide, 7.4" sidewall
A 235/80R18 tire is 32.8 inches (833 mm) tall and 9.3 inches wide. The sidewall is 80% of the width, 7.4 inches, on a 18-inch wheel, and the tire turns about 615 times per mile.
In flotation terms that is about 32.8x9.3R18, closest to the common 33x12.50R18 (33.0"). People often call it a 33-inch tire.
The size most often compared with it is 255/75R18, which is 0.3" taller (+0.8%). At an indicated 60 mph you would be doing 60.5 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 235/80R18 | |
|---|---|---|---|---|---|
| 255/75R18 | 33.1" | 10.0" | 7.5" | +0.8% | |
| 245/75R18 | 32.5" | 9.6" | 7.2" | −1.0% | |
| 255/70R18 | 32.1" | 10.0" | 7.0" | −2.3% | |
| 235/75R18 | 31.9" | 9.3" | 6.9" | −2.8% | |
| 255/80R18 | 34.1" | 10.0" | 8.0" | +3.8% | |
| 245/70R18 | 31.5" | 9.6" | 6.8" | −4.0% |
Sizes within 2% of 32.8" on 16" or 20" or 17" wheels.
| Size | Diameter | Width | Sidewall | vs 235/80R18 | |
|---|---|---|---|---|---|
| 305/70R16 | 32.8" | 12.0" | 8.4" | +0.0% | |
| 325/50R20 | 32.8" | 12.8" | 6.4" | −0.0% | |
| 285/75R16 | 32.8" | 11.2" | 8.4" | +0.1% | |
| 295/55R20 | 32.8" | 11.6" | 6.4" | −0.1% | |
| 235/85R17 | 32.7" | 9.3" | 7.9" | −0.2% | |
| 285/70R17 | 32.7" | 11.2" | 7.9" | −0.3% |
Actual speed when the speedometer is calibrated for 235/80R18.
| Speedometer shows | on 255/75R18 | on 245/75R18 | on 255/70R18 |
|---|---|---|---|
| 30 mph | 30.2 mph | 29.7 mph | 29.3 mph |
| 45 mph | 45.4 mph | 44.5 mph | 44.0 mph |
| 60 mph | 60.5 mph | 59.4 mph | 58.6 mph |
| 70 mph | 70.5 mph | 69.3 mph | 68.4 mph |
32.8 inches (833 mm). The sidewall is 7.4 inches.
9.3 inches (235 mm) section width, measured sidewall to sidewall.
About 32.8x9.3R18; the closest common flotation size is 33x12.50R18 at 33.0".
255/75R18 is +0.8% in diameter, within the common 3% guideline. It is 0.8" wider.