32.0" tall, 12.0" wide, 6.0" sidewall
A 305/50R20 tire is 32.0 inches (813 mm) tall and 12.0 inches wide. The sidewall is 50% of the width, 6.0 inches, on a 20-inch wheel, and the tire turns about 630 times per mile.
In flotation terms that is about 32.0x12.0R20. People often call it a 32-inch tire.
The size most often compared with it is 305/55R20, which is 1.2" taller (+3.8%). At an indicated 60 mph you would be doing 62.3 mph on it, more than the 3% change many shops use as a limit.
| 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 305/50R20 | |
|---|---|---|---|---|---|
| 285/55R20 | 32.3" | 11.2" | 6.2" | +1.0% | |
| 295/50R20 | 31.6" | 11.6" | 5.8" | −1.2% | |
| 315/50R20 | 32.4" | 12.4" | 6.2" | +1.2% | |
| 295/55R20 | 32.8" | 11.6" | 6.4" | +2.4% | |
| 285/50R20 | 31.2" | 11.2" | 5.6" | −2.5% | |
| 325/50R20 | 32.8" | 12.8" | 6.4" | +2.5% | |
| 315/45R20 | 31.2" | 12.4" | 5.6" | −2.6% | |
| 33x12.50R20 | 33.0" | 12.5" | 6.5" | +3.1% | compare |
| 305/45R20 | 30.8" | 12.0" | 5.4" | −3.8% | |
| 305/55R20 | 33.2" | 12.0" | 6.6" | +3.8% | compare |
Sizes within 2% of 32.0" on 18" or 22" wheels.
| Size | Diameter | Width | Sidewall | vs 305/50R20 | |
|---|---|---|---|---|---|
| 255/70R18 | 32.1" | 10.0" | 7.0" | +0.1% | |
| 275/65R18 | 32.1" | 10.8" | 7.0" | +0.2% | |
| 295/60R18 | 31.9" | 11.6" | 7.0" | −0.2% | |
| 315/40R22 | 31.9" | 12.4" | 5.0" | −0.3% | |
| 235/75R18 | 31.9" | 9.3" | 6.9" | −0.4% | |
| 325/40R22 | 32.2" | 12.8" | 5.1" | +0.7% |
Actual speed when the speedometer is calibrated for 305/50R20.
| Speedometer shows | on 305/55R20 | on 33x12.50R20 | on 285/55R20 |
|---|---|---|---|
| 30 mph | 31.1 mph | 30.9 mph | 30.3 mph |
| 45 mph | 46.7 mph | 46.4 mph | 45.5 mph |
| 60 mph | 62.3 mph | 61.9 mph | 60.6 mph |
| 70 mph | 72.6 mph | 72.2 mph | 70.7 mph |
32.0 inches (813 mm). The sidewall is 6.0 inches.
12.0 inches (305 mm) section width, measured sidewall to sidewall.
About 32.0x12.0R20.
305/55R20 is +3.8% in diameter, more than the common 3% guideline, so expect a speedometer error and check clearance. It is 0.0" wider.