33.6" tall, 12.0" wide, 7.8" sidewall
A 305/65R18 tire is 33.6 inches (854 mm) tall and 12.0 inches wide. The sidewall is 65% of the width, 7.8 inches, on a 18-inch wheel, and the tire turns about 600 times per mile.
In flotation terms that is about 33.6x12.0R18. People often call it a 34-inch tire.
The size most often compared with it is 285/70R18, 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 305/65R18 | |
|---|---|---|---|---|---|
| 285/70R18 | 33.7" | 11.2" | 7.9" | +0.3% | |
| 325/60R18 | 33.4" | 12.8" | 7.7" | −0.8% | |
| 295/65R18 | 33.1" | 11.6" | 7.5" | −1.5% | |
| 315/65R18 | 34.1" | 12.4" | 8.1" | +1.5% | |
| 33x12.50R18 | 33.0" | 12.5" | 7.5" | −1.8% | |
| 295/70R18 | 34.3" | 11.6" | 8.1" | +1.9% | |
| 285/65R18 | 32.6" | 11.2" | 7.3" | −3.0% | |
| 325/65R18 | 34.6" | 12.8" | 8.3" | +3.0% | |
| 305/70R18 | 34.8" | 12.0" | 8.4" | +3.6% | |
| 305/60R18 | 32.4" | 12.0" | 7.2" | −3.6% |
Sizes within 2% of 33.6" on 19" or 20" or 17" or 16" wheels.
| Size | Diameter | Width | Sidewall | vs 305/65R18 | |
|---|---|---|---|---|---|
| 265/70R19 | 33.6" | 10.4" | 7.3" | −0.0% | |
| 315/55R20 | 33.6" | 12.4" | 6.8" | +0.1% | |
| 265/65R20 | 33.6" | 10.4" | 6.8" | −0.1% | |
| 265/80R17 | 33.7" | 10.4" | 8.3" | +0.2% | |
| 265/85R16 | 33.7" | 10.4" | 8.9" | +0.4% | |
| 245/75R19 | 33.5" | 9.6" | 7.2" | −0.4% |
Actual speed when the speedometer is calibrated for 305/65R18.
| Speedometer shows | on 285/70R18 | on 325/60R18 | on 295/65R18 |
|---|---|---|---|
| 30 mph | 30.1 mph | 29.8 mph | 29.5 mph |
| 45 mph | 45.1 mph | 44.7 mph | 44.3 mph |
| 60 mph | 60.2 mph | 59.5 mph | 59.1 mph |
| 70 mph | 70.2 mph | 69.5 mph | 68.9 mph |
33.6 inches (854 mm). The sidewall is 7.8 inches.
12.0 inches (305 mm) section width, measured sidewall to sidewall.
About 33.6x12.0R18.
285/70R18 is +0.3% in diameter, within the common 3% guideline. It is 0.8" narrower.