33.2" tall, 12.0" wide, 6.6" sidewall
A 305/55R20 tire is 33.2 inches (844 mm) tall and 12.0 inches wide. The sidewall is 55% of the width, 6.6 inches, on a 20-inch wheel, and the tire turns about 607 times per mile.
In flotation terms that is about 33.2x12.0R20, closest to the common 33x12.50R20 (33.0"). People often call it a 33-inch tire.
The size most often compared with it is 305/50R20, which is 1.2" shorter (−3.6%). At an indicated 60 mph you would be doing 57.8 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 305/55R20 | |
|---|---|---|---|---|---|
| 33x12.50R20 | 33.0" | 12.5" | 6.5" | −0.6% | compare |
| 285/60R20 | 33.5" | 11.2" | 6.7" | +0.8% | |
| 325/50R20 | 32.8" | 12.8" | 6.4" | −1.2% | |
| 295/55R20 | 32.8" | 11.6" | 6.4" | −1.3% | |
| 315/55R20 | 33.6" | 12.4" | 6.8" | +1.3% | |
| 295/60R20 | 33.9" | 11.6" | 7.0" | +2.2% | |
| 315/50R20 | 32.4" | 12.4" | 6.2" | −2.4% | |
| 325/55R20 | 34.1" | 12.8" | 7.0" | +2.6% | |
| 285/55R20 | 32.3" | 11.2" | 6.2" | −2.6% | |
| 305/50R20 | 32.0" | 12.0" | 6.0" | −3.6% | compare |
Sizes within 2% of 33.2" on 22" or 18" wheels.
| Size | Diameter | Width | Sidewall | vs 305/55R20 | |
|---|---|---|---|---|---|
| 285/50R22 | 33.2" | 11.2" | 5.6" | +0.0% | |
| 315/45R22 | 33.2" | 12.4" | 5.6" | −0.1% | |
| 275/70R18 | 33.2" | 10.8" | 7.6" | −0.2% | |
| 295/65R18 | 33.1" | 11.6" | 7.5" | −0.3% | |
| 325/60R18 | 33.4" | 12.8" | 7.7" | +0.4% | |
| 255/75R18 | 33.1" | 10.0" | 7.5" | −0.5% |
Actual speed when the speedometer is calibrated for 305/55R20.
| Speedometer shows | on 305/50R20 | on 275/60R20 | on 33x12.50R20 |
|---|---|---|---|
| 30 mph | 28.9 mph | 29.8 mph | 29.8 mph |
| 45 mph | 43.4 mph | 44.7 mph | 44.7 mph |
| 60 mph | 57.8 mph | 59.6 mph | 59.6 mph |
| 70 mph | 67.5 mph | 69.5 mph | 69.6 mph |
33.2 inches (844 mm). The sidewall is 6.6 inches.
12.0 inches (305 mm) section width, measured sidewall to sidewall.
About 33.2x12.0R20; the closest common flotation size is 33x12.50R20 at 33.0".
305/50R20 is −3.6% in diameter, more than the common 3% guideline, so expect a speedometer error and check clearance. It is 0.0" wider.