ElpiAuto305/55R20 in inches
A 305/55R20 is 33.2″ tall and 12.0″ wide on a 20″ wheel — about a 33.2x12R20 in inch/flotation notation, a 33-inch tire.
Your tire size
e.g. 235/75R15, 33X12.50R15, or 225/45R17 91V
Sizes close to 305/55R20
No standard metric size lands exactly on 305/55R20. The best compromise is 295/55R20 (−1.3% height, −10 mm width); the list is ranked by height and width together, all on a 20″ wheel within ±3%.
| Size | Diameter | Height vs 305/55R20 | Width vs 305/55R20 |
|---|---|---|---|
| 295/55R20 | 32.8″ · 833 mm | −1.3% | −10 mm |
| 315/55R20 | 33.6″ · 855 mm | +1.3% | +10 mm |
| 285/60R20 | 33.5″ · 850 mm | +0.8% | −20 mm |
| 335/50R20 | 33.2″ · 843 mm | −0.1% | +30 mm |
| 295/60R20 | 33.9″ · 862 mm | +2.2% | −10 mm |
305/55R20 dimensions
Computed from the size code; moulded tires vary by brand by roughly 1–3%.
| Dimension | Inches | Millimetres |
|---|---|---|
| Overall diameter | 33.2″ | 844 |
| Section width | 12.01″ | 305 |
| Sidewall height | 6.60″ | 168 |
| Circumference | 104.3″ | 2650 |
| Revolutions per mile | 607 | — |
| Revolutions per km | — | 377 |
The same height on other wheels
If you are changing wheel diameter but want to keep a 33.2″ overall height, these metric sizes come closest (within 2%).
| Wheel | Size | Diameter | Difference |
|---|---|---|---|
| 15″ | 275/85R15 | 33.4″ | +0.6% |
| 16″ | 335/65R16 | 33.1″ | −0.2% |
| 17″ | 275/75R17 | 33.2″ | +0.1% |
| 18″ | 275/70R18 | 33.2″ | −0.2% |
| 22″ | 285/50R22 | 33.2″ | +0.0% |
Wheel width and neighbouring sizes
A 305 mm-wide tire mounts on 9.0–11.5″ wide wheels (the usual approved range; the middle is ideal).
One step down is 33X12.50R20: −0.6% in diameter. With a speedometer calibrated for 305/55R20, an indicated 60 mph would be 59.6 mph on 33X12.50R20.
One step up is 35X12.50R20: +5.4% in diameter. With a speedometer calibrated for 305/55R20, an indicated 60 mph would be 63.2 mph on 35X12.50R20.
Figures are geometric: overall diameter = wheel + 2 × sidewall, 25.4 mm per inch. Check the tire maker's data sheet for the exact moulded size before buying.