31.8" tall, 12.0" wide, 8.4" sidewall
A 305/70R15 tire is 31.8 inches (808 mm) tall and 12.0 inches wide. The sidewall is 70% of the width, 8.4 inches, on a 15-inch wheel, and the tire turns about 634 times per mile.
In flotation terms that is about 31.8x12.0R15, closest to the common 32x11.50R15 (32.0"). People often call it a 32-inch tire.
The size most often compared with it is 285/75R15, which is 0.0" taller (+0.1%). At an indicated 60 mph you would be doing 60.0 mph on it.
| Current | New | Difference |
|---|
| Shows | Actual speed |
|---|
Same 15" wheel, within 20 mm of width and 10 points of aspect ratio.
| Size | Diameter | Width | Sidewall | vs 305/70R15 | |
|---|---|---|---|---|---|
| 285/75R15 | 31.8" | 11.2" | 8.4" | +0.1% | |
| 32x11.50R15 | 32.0" | 11.5" | 8.5" | +0.6% | |
| 295/70R15 | 31.3" | 11.6" | 8.1" | −1.7% | |
| 315/70R15 | 32.4" | 12.4" | 8.7" | +1.7% | |
| 295/75R15 | 32.4" | 11.6" | 8.7" | +1.9% | |
| 285/70R15 | 30.7" | 11.2" | 7.9" | −3.5% | |
| 33x12.50R15 | 33.0" | 12.5" | 9.0" | +3.7% | |
| 325/60R15 | 30.4" | 12.8" | 7.7" | −4.6% | |
| 295/65R15 | 30.1" | 11.6" | 7.5" | −5.4% | |
| 315/75R15 | 33.6" | 12.4" | 9.3" | +5.6% |
Sizes within 2% of 31.8" on 17" or 16" wheels.
| Size | Diameter | Width | Sidewall | vs 305/70R15 | |
|---|---|---|---|---|---|
| 235/80R17 | 31.8" | 9.3" | 7.4" | −0.0% | |
| 315/60R17 | 31.9" | 12.4" | 7.4" | +0.2% | |
| 235/85R16 | 31.7" | 9.3" | 7.9" | −0.3% | |
| 285/70R16 | 31.7" | 11.2" | 7.9" | −0.3% | |
| 265/75R16 | 31.6" | 10.4" | 7.8" | −0.5% | |
| 265/70R17 | 31.6" | 10.4" | 7.3" | −0.6% |
Actual speed when the speedometer is calibrated for 305/70R15.
| Speedometer shows | on 285/75R15 | on 32x11.50R15 | on 295/70R15 |
|---|---|---|---|
| 30 mph | 30.0 mph | 30.2 mph | 29.5 mph |
| 45 mph | 45.0 mph | 45.3 mph | 44.2 mph |
| 60 mph | 60.0 mph | 60.4 mph | 59.0 mph |
| 70 mph | 70.0 mph | 70.4 mph | 68.8 mph |
31.8 inches (808 mm). The sidewall is 8.4 inches.
12.0 inches (305 mm) section width, measured sidewall to sidewall.
About 31.8x12.0R15; the closest common flotation size is 32x11.50R15 at 32.0".
285/75R15 is +0.1% in diameter, within the common 3% guideline. It is 0.8" narrower.