33.4" tall, 12.8" wide, 7.7" sidewall
A 325/60R18 tire is 33.4 inches (847 mm) tall and 12.8 inches wide. The sidewall is 60% of the width, 7.7 inches, on a 18-inch wheel, and the tire turns about 605 times per mile.
In flotation terms that is about 33.4x12.8R18, closest to the common 33x12.50R18 (33.0"). People often call it a 33-inch tire.
The size most often compared with it is 305/65R18, which is 0.3" taller (+0.8%). At an indicated 60 mph you would be doing 60.5 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 325/60R18 | |
|---|---|---|---|---|---|
| 305/65R18 | 33.6" | 12.0" | 7.8" | +0.8% | |
| 33x12.50R18 | 33.0" | 12.5" | 7.5" | −1.1% | |
| 315/65R18 | 34.1" | 12.4" | 8.1" | +2.3% | |
| 305/60R18 | 32.4" | 12.0" | 7.2" | −2.8% | |
| 325/65R18 | 34.6" | 12.8" | 8.3" | +3.8% | |
| 305/70R18 | 34.8" | 12.0" | 8.4" | +4.4% | |
| 35x12.50R18 | 35.0" | 12.5" | 8.5" | +4.9% | |
| 315/70R18 | 35.4" | 12.4" | 8.7" | +6.0% | |
| 305/55R18 | 31.2" | 12.0" | 6.6" | −6.4% | |
| 325/70R18 | 35.9" | 12.8" | 9.0" | +7.7% |
Sizes within 2% of 33.4" on 16" or 17" or 20" wheels.
| Size | Diameter | Width | Sidewall | vs 325/60R18 | |
|---|---|---|---|---|---|
| 315/70R16 | 33.4" | 12.4" | 8.7" | +0.0% | |
| 275/80R16 | 33.3" | 10.8" | 8.7" | −0.1% | |
| 245/85R17 | 33.4" | 9.6" | 8.2" | +0.1% | |
| 295/75R16 | 33.4" | 11.6" | 8.7" | +0.2% | |
| 295/70R17 | 33.3" | 11.6" | 8.1" | −0.3% | |
| 285/60R20 | 33.5" | 11.2" | 6.7" | +0.3% |
Actual speed when the speedometer is calibrated for 325/60R18.
| Speedometer shows | on 305/65R18 | on 33x12.50R18 | on 315/65R18 |
|---|---|---|---|
| 30 mph | 30.2 mph | 29.7 mph | 30.7 mph |
| 45 mph | 45.3 mph | 44.5 mph | 46.0 mph |
| 60 mph | 60.5 mph | 59.4 mph | 61.4 mph |
| 70 mph | 70.5 mph | 69.3 mph | 71.6 mph |
33.4 inches (847 mm). The sidewall is 7.7 inches.
12.8 inches (325 mm) section width, measured sidewall to sidewall.
About 33.4x12.8R18; the closest common flotation size is 33x12.50R18 at 33.0".
305/65R18 is +0.8% in diameter, within the common 3% guideline. It is 0.8" narrower.