30.8" tall, 12.0" wide, 5.4" sidewall
A 305/45R20 tire is 30.8 inches (783 mm) tall and 12.0 inches wide. The sidewall is 45% of the width, 5.4 inches, on a 20-inch wheel, and the tire turns about 655 times per mile.
In flotation terms that is about 30.8x12.0R20. People often call it a 31-inch tire.
The size most often compared with it is 295/45R20, which is 0.4" shorter (−1.2%). 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 305/45R20 | |
|---|---|---|---|---|---|
| 295/45R20 | 30.5" | 11.6" | 5.2" | −1.2% | |
| 315/45R20 | 31.2" | 12.4" | 5.6" | +1.2% | |
| 285/50R20 | 31.2" | 11.2" | 5.6" | +1.3% | |
| 295/50R20 | 31.6" | 11.6" | 5.8" | +2.6% | |
| 315/40R20 | 29.9" | 12.4" | 5.0" | −2.9% | |
| 305/40R20 | 29.6" | 12.0" | 4.8" | −3.9% | |
| 305/50R20 | 32.0" | 12.0" | 6.0" | +3.9% | |
| 295/40R20 | 29.3" | 11.6" | 4.6" | −4.9% | |
| 285/55R20 | 32.3" | 11.2" | 6.2" | +5.0% | |
| 315/50R20 | 32.4" | 12.4" | 6.2" | +5.2% |
Sizes within 2% of 30.8" on 18" or 22" wheels.
| Size | Diameter | Width | Sidewall | vs 305/45R20 | |
|---|---|---|---|---|---|
| 295/55R18 | 30.8" | 11.6" | 6.4" | −0.1% | |
| 325/35R22 | 31.0" | 12.8" | 4.5" | +0.5% | |
| 285/40R22 | 31.0" | 11.2" | 4.5" | +0.5% | |
| 275/60R18 | 31.0" | 10.8" | 6.5" | +0.6% | |
| 245/65R18 | 30.5" | 9.6" | 6.3" | −0.9% | |
| 305/35R22 | 30.4" | 12.0" | 4.2" | −1.3% |
Actual speed when the speedometer is calibrated for 305/45R20.
| Speedometer shows | on 295/45R20 | on 315/45R20 | on 285/50R20 |
|---|---|---|---|
| 30 mph | 29.7 mph | 30.3 mph | 30.4 mph |
| 45 mph | 44.5 mph | 45.5 mph | 45.6 mph |
| 60 mph | 59.3 mph | 60.7 mph | 60.8 mph |
| 70 mph | 69.2 mph | 70.8 mph | 70.9 mph |
30.8 inches (783 mm). The sidewall is 5.4 inches.
12.0 inches (305 mm) section width, measured sidewall to sidewall.
About 30.8x12.0R20.
295/45R20 is −1.2% in diameter, within the common 3% guideline. It is 0.4" narrower.