35.9" tall, 12.8" wide, 9.0" sidewall
A 325/70R18 tire is 35.9 inches (912 mm) tall and 12.8 inches wide. The sidewall is 70% of the width, 9.0 inches, on a 18-inch wheel, and the tire turns about 562 times per mile.
In flotation terms that is about 35.9x12.8R18. People often call it a 36-inch tire.
The size most often compared with it is 305/75R18, which is 0.1" taller (+0.3%). At an indicated 60 mph you would be doing 60.2 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 325/70R18 | |
|---|---|---|---|---|---|
| 305/75R18 | 36.0" | 12.0" | 9.0" | +0.3% | |
| 315/70R18 | 35.4" | 12.4" | 8.7" | −1.5% | |
| 35x12.50R18 | 35.0" | 12.5" | 8.5" | −2.5% | |
| 37x12.50R18 | 37.0" | 12.5" | 9.5" | +3.0% | |
| 37x13.50R18 | 37.0" | 13.5" | 9.5" | +3.0% | |
| 305/70R18 | 34.8" | 12.0" | 8.4" | −3.1% | |
| 325/65R18 | 34.6" | 12.8" | 8.3" | −3.6% | |
| 315/65R18 | 34.1" | 12.4" | 8.1" | −5.0% | |
| 305/65R18 | 33.6" | 12.0" | 7.8" | −6.4% | |
| 325/60R18 | 33.4" | 12.8" | 7.7" | −7.1% |
Sizes within 2% of 35.9" on 16" or 19" or 17" or 20" wheels.
| Size | Diameter | Width | Sidewall | vs 325/70R18 | |
|---|---|---|---|---|---|
| 315/80R16 | 35.8" | 12.4" | 9.9" | −0.2% | |
| 305/70R19 | 35.8" | 12.0" | 8.4" | −0.3% | |
| 285/85R17 | 36.1" | 11.2" | 9.5" | +0.4% | |
| 285/70R20 | 35.7" | 11.2" | 7.9" | −0.6% | |
| 315/65R20 | 36.1" | 12.4" | 8.1" | +0.6% | |
| 265/75R20 | 35.6" | 10.4" | 7.8" | −0.7% |
Actual speed when the speedometer is calibrated for 325/70R18.
| Speedometer shows | on 305/75R18 | on 315/70R18 | on 35x12.50R18 |
|---|---|---|---|
| 30 mph | 30.1 mph | 29.5 mph | 29.2 mph |
| 45 mph | 45.1 mph | 44.3 mph | 43.9 mph |
| 60 mph | 60.2 mph | 59.1 mph | 58.5 mph |
| 70 mph | 70.2 mph | 68.9 mph | 68.2 mph |
35.9 inches (912 mm). The sidewall is 9.0 inches.
12.8 inches (325 mm) section width, measured sidewall to sidewall.
About 35.9x12.8R18.
305/75R18 is +0.3% in diameter, within the common 3% guideline. It is 0.8" narrower.