30.7" tall, 9.3" wide, 7.9" sidewall
A 235/85R15 tire is 30.7 inches (781 mm) tall and 9.3 inches wide. The sidewall is 85% of the width, 7.9 inches, on a 15-inch wheel, and the tire turns about 656 times per mile.
In flotation terms that is about 30.7x9.3R15, closest to the common 31x10.50R15 (31.0"). People often call it a 31-inch tire.
The size most often compared with it is 255/75R15, which is 0.7" shorter (−2.2%). At an indicated 60 mph you would be doing 58.7 mph on it.
| Current | New | Difference |
|---|
| Shows | Actual speed |
|---|
Same 15" wheel, within 20 mm of width and 10 points of aspect ratio.
| Size | Diameter | Width | Sidewall | vs 235/85R15 | |
|---|---|---|---|---|---|
| 255/75R15 | 30.1" | 10.0" | 7.5" | −2.2% | |
| 30x9.50R15 | 30.0" | 9.5" | 7.5" | −2.4% | |
| 245/75R15 | 29.5" | 9.6" | 7.2" | −4.1% | |
| 255/85R15 | 32.1" | 10.0" | 8.5" | +4.4% | |
| 235/75R15 | 28.9" | 9.3" | 6.9" | −6.0% | |
| 215/80R15 | 28.5" | 8.5" | 6.8" | −7.1% | |
| 215/75R15 | 27.7" | 8.5" | 6.3" | −9.9% |
Sizes within 2% of 30.7" on 17" or 16" wheels.
| Size | Diameter | Width | Sidewall | vs 235/85R15 | |
|---|---|---|---|---|---|
| 315/55R17 | 30.6" | 12.4" | 6.8" | −0.3% | |
| 265/70R16 | 30.6" | 10.4" | 7.3" | −0.4% | |
| 285/65R16 | 30.6" | 11.2" | 7.3" | −0.5% | |
| 265/65R17 | 30.6" | 10.4" | 6.8" | −0.5% | |
| 245/70R17 | 30.5" | 9.6" | 6.8" | −0.7% | |
| 245/75R16 | 30.5" | 9.6" | 7.2" | −0.8% |
Actual speed when the speedometer is calibrated for 235/85R15.
| Speedometer shows | on 255/75R15 | on 30x9.50R15 | on 245/75R15 |
|---|---|---|---|
| 30 mph | 29.3 mph | 29.3 mph | 28.8 mph |
| 45 mph | 44.0 mph | 43.9 mph | 43.2 mph |
| 60 mph | 58.7 mph | 58.6 mph | 57.5 mph |
| 70 mph | 68.5 mph | 68.3 mph | 67.1 mph |
30.7 inches (781 mm). The sidewall is 7.9 inches.
9.3 inches (235 mm) section width, measured sidewall to sidewall.
About 30.7x9.3R15; the closest common flotation size is 31x10.50R15 at 31.0".
255/75R15 is −2.2% in diameter, within the common 3% guideline. It is 0.8" wider.