32.4" tall, 12.0" wide, 7.2" sidewall
A 305/60R18 tire is 32.4 inches (823 mm) tall and 12.0 inches wide. The sidewall is 60% of the width, 7.2 inches, on a 18-inch wheel, and the tire turns about 622 times per mile.
In flotation terms that is about 32.4x12.0R18, closest to the common 33x12.50R18 (33.0"). People often call it a 32-inch tire.
The size most often compared with it is 275/65R18, which is 0.3" shorter (−1.0%). At an indicated 60 mph you would be doing 59.4 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 305/60R18 | |
|---|---|---|---|---|---|
| 285/65R18 | 32.6" | 11.2" | 7.3" | +0.5% | |
| 295/60R18 | 31.9" | 11.6" | 7.0" | −1.5% | |
| 33x12.50R18 | 33.0" | 12.5" | 7.5" | +1.8% | |
| 295/65R18 | 33.1" | 11.6" | 7.5" | +2.1% | |
| 285/60R18 | 31.5" | 11.2" | 6.7" | −2.9% | |
| 325/60R18 | 33.4" | 12.8" | 7.7" | +2.9% | |
| 305/65R18 | 33.6" | 12.0" | 7.8" | +3.7% | |
| 305/55R18 | 31.2" | 12.0" | 6.6" | −3.7% | |
| 285/70R18 | 33.7" | 11.2" | 7.9" | +4.0% | |
| 295/55R18 | 30.8" | 11.6" | 6.4" | −5.0% |
Sizes within 2% of 32.4" on 20" or 16" or 17" or 19" wheels.
| Size | Diameter | Width | Sidewall | vs 305/60R18 | |
|---|---|---|---|---|---|
| 315/50R20 | 32.4" | 12.4" | 6.2" | −0.0% | |
| 245/85R16 | 32.4" | 9.6" | 8.2" | −0.0% | |
| 245/80R17 | 32.4" | 9.6" | 7.7" | +0.1% | |
| 285/55R20 | 32.3" | 11.2" | 6.2" | −0.2% | |
| 245/70R19 | 32.5" | 9.6" | 6.8" | +0.3% | |
| 265/60R20 | 32.5" | 10.4" | 6.3" | +0.3% |
Actual speed when the speedometer is calibrated for 305/60R18.
| Speedometer shows | on 275/65R18 | on 275/70R18 | on 285/65R18 |
|---|---|---|---|
| 30 mph | 29.7 mph | 30.7 mph | 30.2 mph |
| 45 mph | 44.5 mph | 46.0 mph | 45.2 mph |
| 60 mph | 59.4 mph | 61.4 mph | 60.3 mph |
| 70 mph | 69.3 mph | 71.6 mph | 70.4 mph |
32.4 inches (823 mm). The sidewall is 7.2 inches.
12.0 inches (305 mm) section width, measured sidewall to sidewall.
About 32.4x12.0R18; the closest common flotation size is 33x12.50R18 at 33.0".
275/65R18 is −1.0% in diameter, within the common 3% guideline. It is 1.2" narrower.