31.9" tall, 9.3" wide, 6.9" sidewall
A 235/75R18 tire is 31.9 inches (810 mm) tall and 9.3 inches wide. The sidewall is 75% of the width, 6.9 inches, on a 18-inch wheel, and the tire turns about 633 times per mile.
In flotation terms that is about 31.9x9.3R18. People often call it a 32-inch tire.
The size most often compared with it is 255/70R18, which is 0.2" taller (+0.6%). At an indicated 60 mph you would be doing 60.3 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 235/75R18 | |
|---|---|---|---|---|---|
| 255/70R18 | 32.1" | 10.0" | 7.0" | +0.6% | |
| 245/70R18 | 31.5" | 9.6" | 6.8" | −1.2% | |
| 245/75R18 | 32.5" | 9.6" | 7.2" | +1.9% | |
| 235/80R18 | 32.8" | 9.3" | 7.4" | +2.9% | |
| 255/75R18 | 33.1" | 10.0" | 7.5" | +3.7% | |
| 245/65R18 | 30.5" | 9.6" | 6.3" | −4.2% | |
| 255/80R18 | 34.1" | 10.0" | 8.0" | +6.9% |
Sizes within 2% of 31.9" on 17" or 20" or 16" wheels.
| Size | Diameter | Width | Sidewall | vs 235/75R18 | |
|---|---|---|---|---|---|
| 315/60R17 | 31.9" | 12.4" | 7.4" | +0.0% | |
| 275/55R20 | 31.9" | 10.8" | 6.0" | +0.1% | |
| 235/80R17 | 31.8" | 9.3" | 7.4" | −0.2% | |
| 305/50R20 | 32.0" | 12.0" | 6.0" | +0.4% | |
| 235/85R16 | 31.7" | 9.3" | 7.9" | −0.5% | |
| 255/60R20 | 32.0" | 10.0" | 6.0" | +0.5% |
Actual speed when the speedometer is calibrated for 235/75R18.
| Speedometer shows | on 255/70R18 | on 245/70R18 | on 245/75R18 |
|---|---|---|---|
| 30 mph | 30.2 mph | 29.6 mph | 30.6 mph |
| 45 mph | 45.3 mph | 44.5 mph | 45.8 mph |
| 60 mph | 60.3 mph | 59.3 mph | 61.1 mph |
| 70 mph | 70.4 mph | 69.2 mph | 71.3 mph |
31.9 inches (810 mm). The sidewall is 6.9 inches.
9.3 inches (235 mm) section width, measured sidewall to sidewall.
About 31.9x9.3R18.
255/70R18 is +0.6% in diameter, within the common 3% guideline. It is 0.8" wider.