36.4" tall, 10.8" wide, 9.2" sidewall
A 275/85R18 tire is 36.4 inches (925 mm) tall and 10.8 inches wide. The sidewall is 85% of the width, 9.2 inches, on a 18-inch wheel, and the tire turns about 554 times per mile.
In flotation terms that is about 36.4x10.8R18, closest to the common 37x12.50R18 (37.0"). People often call it a 36-inch tire.
The size most often compared with it is 285/80R18, which is 0.5" shorter (−1.2%). At an indicated 60 mph you would be doing 59.3 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 275/85R18 | |
|---|---|---|---|---|---|
| 285/80R18 | 36.0" | 11.2" | 9.0" | −1.2% | |
| 295/75R18 | 35.4" | 11.6" | 8.7" | −2.7% | |
| 275/80R18 | 35.3" | 10.8" | 8.7" | −3.0% | |
| 285/75R18 | 34.8" | 11.2" | 8.4" | −4.3% | |
| 265/80R18 | 34.7" | 10.4" | 8.3" | −4.7% | |
| 275/75R18 | 34.2" | 10.8" | 8.1" | −5.9% | |
| 255/80R18 | 34.1" | 10.0" | 8.0" | −6.4% | |
| 265/75R18 | 33.6" | 10.4" | 7.8" | −7.6% | |
| 255/75R18 | 33.1" | 10.0" | 7.5" | −9.2% |
Sizes within 2% of 36.4" on 16" or 20" or 17" wheels.
| Size | Diameter | Width | Sidewall | vs 275/85R18 | |
|---|---|---|---|---|---|
| 325/80R16 | 36.5" | 12.8" | 10.2" | +0.2% | |
| 295/70R20 | 36.3" | 11.6" | 8.1" | −0.4% | |
| 275/75R20 | 36.2" | 10.8" | 8.1" | −0.5% | |
| 315/65R20 | 36.1" | 12.4" | 8.1" | −0.8% | |
| 285/85R17 | 36.1" | 11.2" | 9.5" | −0.9% | |
| 315/80R16 | 35.8" | 12.4" | 9.9" | −1.5% |
Actual speed when the speedometer is calibrated for 275/85R18.
| Speedometer shows | on 285/80R18 | on 295/75R18 | on 275/80R18 |
|---|---|---|---|
| 30 mph | 29.6 mph | 29.2 mph | 29.1 mph |
| 45 mph | 44.4 mph | 43.8 mph | 43.7 mph |
| 60 mph | 59.3 mph | 58.4 mph | 58.2 mph |
| 70 mph | 69.1 mph | 68.1 mph | 67.9 mph |
36.4 inches (925 mm). The sidewall is 9.2 inches.
10.8 inches (275 mm) section width, measured sidewall to sidewall.
About 36.4x10.8R18; the closest common flotation size is 37x12.50R18 at 37.0".
285/80R18 is −1.2% in diameter, within the common 3% guideline. It is 0.4" wider.