31.2" tall, 12.4" wide, 5.6" sidewall
A 315/45R20 tire is 31.2 inches (792 mm) tall and 12.4 inches wide. The sidewall is 45% of the width, 5.6 inches, on a 20-inch wheel, and the tire turns about 647 times per mile.
In flotation terms that is about 31.2x12.4R20. People often call it a 31-inch tire.
The size most often compared with it is 305/45R20, which is 0.4" shorter (−1.1%). At an indicated 60 mph you would be doing 59.3 mph on it.
| Current | New | Difference |
|---|
| Shows | Actual speed |
|---|
Same 20" wheel, within 20 mm of width and 10 points of aspect ratio.
| Size | Diameter | Width | Sidewall | vs 315/45R20 | |
|---|---|---|---|---|---|
| 305/45R20 | 30.8" | 12.0" | 5.4" | −1.1% | |
| 295/50R20 | 31.6" | 11.6" | 5.8" | +1.5% | |
| 295/45R20 | 30.5" | 11.6" | 5.2" | −2.3% | |
| 305/50R20 | 32.0" | 12.0" | 6.0" | +2.7% | |
| 315/40R20 | 29.9" | 12.4" | 5.0" | −4.0% | |
| 315/50R20 | 32.4" | 12.4" | 6.2" | +4.0% | |
| 305/40R20 | 29.6" | 12.0" | 4.8" | −5.0% | |
| 295/55R20 | 32.8" | 11.6" | 6.4" | +5.2% | |
| 325/50R20 | 32.8" | 12.8" | 6.4" | +5.2% | |
| 33x12.50R20 | 33.0" | 12.5" | 6.5" | +5.9% |
Sizes within 2% of 31.2" on 18" or 22" wheels.
| Size | Diameter | Width | Sidewall | vs 315/45R20 | |
|---|---|---|---|---|---|
| 305/55R18 | 31.2" | 12.0" | 6.6" | +0.2% | |
| 295/40R22 | 31.3" | 11.6" | 4.6" | +0.4% | |
| 275/60R18 | 31.0" | 10.8" | 6.5" | −0.5% | |
| 285/40R22 | 31.0" | 11.2" | 4.5" | −0.6% | |
| 325/35R22 | 31.0" | 12.8" | 4.5" | −0.7% | |
| 265/45R22 | 31.4" | 10.4" | 4.7" | +0.7% |
Actual speed when the speedometer is calibrated for 315/45R20.
| Speedometer shows | on 305/45R20 | on 295/50R20 | on 295/45R20 |
|---|---|---|---|
| 30 mph | 29.7 mph | 30.4 mph | 29.3 mph |
| 45 mph | 44.5 mph | 45.7 mph | 44.0 mph |
| 60 mph | 59.3 mph | 60.9 mph | 58.6 mph |
| 70 mph | 69.2 mph | 71.0 mph | 68.4 mph |
31.2 inches (792 mm). The sidewall is 5.6 inches.
12.4 inches (315 mm) section width, measured sidewall to sidewall.
About 31.2x12.4R20.
305/45R20 is −1.1% in diameter, within the common 3% guideline. It is 0.4" narrower.