30.3" tall, 11.2" wide, 6.2" sidewall
A 285/55R18 tire is 30.3 inches (771 mm) tall and 11.2 inches wide. The sidewall is 55% of the width, 6.2 inches, on a 18-inch wheel, and the tire turns about 665 times per mile.
In flotation terms that is about 30.3x11.2R18. People often call it a 30-inch tire.
The size most often compared with it is 275/55R18, which is 0.4" shorter (−1.4%). At an indicated 60 mph you would be doing 59.1 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 285/55R18 | |
|---|---|---|---|---|---|
| 275/55R18 | 29.9" | 10.8" | 6.0" | −1.4% | |
| 295/55R18 | 30.8" | 11.6" | 6.4" | +1.4% | |
| 275/60R18 | 31.0" | 10.8" | 6.5" | +2.1% | |
| 265/55R18 | 29.5" | 10.4" | 5.7" | −2.9% | |
| 305/55R18 | 31.2" | 12.0" | 6.6" | +2.9% | |
| 285/50R18 | 29.2" | 11.2" | 5.6" | −3.7% | |
| 285/60R18 | 31.5" | 11.2" | 6.7" | +3.7% | |
| 265/65R18 | 31.6" | 10.4" | 6.8" | +4.0% | |
| 275/50R18 | 28.8" | 10.8" | 5.4" | −5.0% | |
| 295/60R18 | 31.9" | 11.6" | 7.0" | +5.3% |
Sizes within 2% of 30.3" on 16" or 17" or 20" wheels.
| Size | Diameter | Width | Sidewall | vs 285/55R18 | |
|---|---|---|---|---|---|
| 215/85R16 | 30.4" | 8.5" | 7.2" | +0.2% | |
| 225/75R17 | 30.3" | 8.9" | 6.6" | −0.2% | |
| 295/45R20 | 30.5" | 11.6" | 5.2" | +0.4% | |
| 285/60R17 | 30.5" | 11.2" | 6.7" | +0.4% | |
| 245/75R16 | 30.5" | 9.6" | 7.2" | +0.4% | |
| 305/55R17 | 30.2" | 12.0" | 6.6" | −0.4% |
Actual speed when the speedometer is calibrated for 285/55R18.
| Speedometer shows | on 275/55R18 | on 295/55R18 | on 275/60R18 |
|---|---|---|---|
| 30 mph | 29.6 mph | 30.4 mph | 30.6 mph |
| 45 mph | 44.4 mph | 45.6 mph | 46.0 mph |
| 60 mph | 59.1 mph | 60.9 mph | 61.3 mph |
| 70 mph | 69.0 mph | 71.0 mph | 71.5 mph |
30.3 inches (771 mm). The sidewall is 6.2 inches.
11.2 inches (285 mm) section width, measured sidewall to sidewall.
About 30.3x11.2R18.
275/55R18 is −1.4% in diameter, within the common 3% guideline. It is 0.4" narrower.