285/55R20 tire size in inches and millimeters
285/55R20 measures 32.34 inches in overall diameter, 11.22 inches in section width, with a 6.17 inch sidewall.
Every dimension
| Size | In inches | In millimetres |
|---|---|---|
| Overall diameter | 32.34 in | 821.5 mm |
| Section width | 11.22 in | 285 mm |
| Sidewall height | 6.17 in | 156.8 mm |
| Circumference | 101.61 in | 2,580.8 mm |
| Revolutions per mile | 623.6 per mile | 387.5 per km |
Sizes that fit the same wheel
These sizes share a 20 inch wheel diameter and sit within 3% of 285/55R20 in overall diameter, which is the range a swap stays inside without recalibrating anything.
The percentage difference in overall diameter is the speedometer error: a tire 2% taller makes an indicated 60 mph a true 61.2 mph. They are the same number, so it is shown once.
| Alternate size | Overall diameter | Difference (in) | Difference (%) | Width difference (in) |
|---|---|---|---|---|
| 185/85R20 | 32.38 | 0.04 | 0.12 | -3.94 |
| 195/80R20 | 32.28 | -0.06 | -0.18 | -3.54 |
| 225/70R20 | 32.40 | 0.06 | 0.18 | -2.36 |
| 315/50R20 | 32.40 | 0.06 | 0.18 | 1.18 |
| 345/45R20 | 32.22 | -0.12 | -0.37 | 2.36 |
| 265/60R20 | 32.52 | 0.18 | 0.55 | -0.79 |
| 245/65R20 | 32.54 | 0.20 | 0.61 | -1.57 |
| 205/75R20 | 32.11 | -0.24 | -0.73 | -3.15 |
| 355/45R20 | 32.58 | 0.24 | 0.73 | 2.76 |
| 255/60R20 | 32.05 | -0.30 | -0.91 | -1.18 |
| 235/65R20 | 32.03 | -0.32 | -0.97 | -1.97 |
| 305/50R20 | 32.01 | -0.33 | -1.03 | 0.79 |
| 215/75R20 | 32.70 | 0.35 | 1.10 | -2.76 |
| 275/55R20 | 31.91 | -0.43 | -1.34 | -0.39 |
| 295/55R20 | 32.78 | 0.43 | 1.34 | 0.39 |
| 325/50R20 | 32.80 | 0.45 | 1.40 | 1.57 |
| 335/45R20 | 31.87 | -0.47 | -1.46 | 1.97 |
| 215/70R20 | 31.85 | -0.49 | -1.52 | -2.76 |
| 205/80R20 | 32.91 | 0.57 | 1.77 | -3.15 |
| 235/70R20 | 32.95 | 0.61 | 1.89 | -1.97 |
| 275/60R20 | 32.99 | 0.65 | 2.01 | -0.39 |
| 185/80R20 | 31.65 | -0.69 | -2.13 | -3.94 |
| 195/85R20 | 33.05 | 0.71 | 2.19 | -3.54 |
| 255/65R20 | 33.05 | 0.71 | 2.19 | -1.18 |
| 295/50R20 | 31.61 | -0.73 | -2.25 | 0.39 |
| 245/60R20 | 31.57 | -0.77 | -2.37 | -1.57 |
| 195/75R20 | 31.52 | -0.83 | -2.56 | -3.54 |
| 225/65R20 | 31.52 | -0.83 | -2.56 | -2.36 |
| 325/45R20 | 31.52 | -0.83 | -2.56 | 1.57 |
| 335/50R20 | 33.19 | 0.85 | 2.62 | 1.97 |
| 265/55R20 | 31.48 | -0.87 | -2.68 | -0.79 |
| 305/55R20 | 33.21 | 0.87 | 2.68 | 0.79 |
| 225/75R20 | 33.29 | 0.94 | 2.92 | -2.36 |
How this is worked out
sidewall height in millimetres = section width × aspect ratio ÷ 100
overall diameter in inches = wheel diameter + (section width × aspect ratio × 2) ÷ 2540
section width in inches = section width in millimetres ÷ 25.4
circumference in inches = π × overall diameter
revolutions per mile = 63360 ÷ circumference in inches
The divisor is 2540, not the 2550 some converters publish. Two sidewalls in inches are 2 × width × aspect ÷ (100 × 25.4), and the rounding costs about 0.07 inches at 34 inches.
For 285/55R20: the sidewall is 156.8 millimetres, two of them are 12.34 inches, and adding the 20 inch wheel gives 32.34 inches overall.
Questions
What size is 285/55R20 in inches?
32.34 inches in overall diameter, 11.22 inches in section width, with a 6.17 inch sidewall.
How tall is a 285/55R20 tire?
32.34 inches, which is 821.5 millimetres.
What do the numbers in 285/55R20 mean?
285 is the section width in millimetres, 55 is the sidewall height as a percentage of that width, and 20 is the wheel diameter in inches. Overall diameter is the wheel diameter plus two sidewalls: 32.34 inches.
Does 285/55R20 fit a 20-inch wheel?
Yes — the 20 in a metric tire size *is* the wheel diameter, so 285/55R20 is made for a 20 inch wheel. Rim width is a separate question the sidewall code does not answer.
What tire sizes are equivalent to 285/55R20?
185/85R20, 195/80R20, 225/70R20 are the closest by overall diameter, all on the same 20 inch wheel.
Fitting a size is not only a matter of diameter. Rim width, load rating, speed rating and clearance all decide whether a size works on a given vehicle, and none of them can be read off the sidewall code alone.