285/55R20 tire size
A 285/55R20 tire is 32.3 inches (822 mm) tall and 11.2 inches (285 mm) wide, for a 20-inch wheel. Each sidewall is 6.2 inches (157 mm), 55% of the width, and the tire makes about 624 revolutions a mile.
Sources checked
| Dimension | 285/55R20 |
|---|---|
| Overall diameter | 32.34 in (822 mm) |
| Section width | 11.22 in (285 mm) |
| Sidewall height | 6.17 in (157 mm) |
| Aspect ratio | 55% |
| Rim diameter | 20 in |
| Circumference | 101.6 in (2,581 mm) |
| Revolutions per mile | 624 |
| Revolutions per km | 387 |
Compare 285/55R20 with another size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
62.1mph
+3.5% · the speedometer reads low
- Height
- +1.12 in (+29 mm)
- Width
- 0.00 in (0 mm)
- Ground clearance
- +0.56 in (+14 mm)
- Each side, same wheel
- 0.00 in (0 mm)
285/55R20 and 285/60R20 side by side
| Dimension | 285/55R20 | 285/60R20 | Change |
|---|---|---|---|
| Overall diameter | 32.34 in (822 mm) | 33.46 in (850 mm) | +1.12 in (+28 mm) |
| Section width | 11.22 in (285 mm) | 11.22 in (285 mm) | 0.00 in (0 mm) |
| Sidewall height | 6.17 in (157 mm) | 6.73 in (171 mm) | +0.56 in (+14 mm) |
| Aspect ratio | 55% | 60% | |
| Rim diameter | 20 in | 20 in | |
| Circumference | 101.6 in | 105.1 in | +3.5 in |
| Revolutions per mile | 624 | 603 | −21 |
| Revolutions per km | 387 | 374 | −13 |
The working
- 285/55R20: sidewall = 285 mm × 55% = 156.8 mm = 6.17 in.
- Diameter = rim + 2 × sidewall = 20 + 2 × 6.17 = 32.34 in (822 mm).
- Circumference = π × 32.34 = 101.6 in; revolutions per mile = 63,360 ÷ 101.6 = 624.
- 285/60R20: sidewall = 285 mm × 60% = 171.0 mm = 6.73 in.
- Diameter = rim + 2 × sidewall = 20 + 2 × 6.73 = 33.46 in (850 mm).
- Circumference = π × 33.46 = 105.1 in; revolutions per mile = 63,360 ÷ 105.1 = 603.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 33.46 ÷ 32.34 = 62.1 mph.
- Ground clearance. Half the change in diameter: (33.46 − 32.34) ÷ 2 = +0.56 in.
Where the 285/55R20 numbers come from
The section width is 285 mm (11.22 inches), and each sidewall is 55% of it: 156.8 mm, or 6.17 inches. Two sidewalls and the 20-inch rim make 32.34 inches (822 mm).
One turn covers π × 32.34 = 101.6 inches, so the tire turns 624 times a mile and 387 times a kilometer.
What tire makers publish for 285/55R20
Inflated on the maker’s measuring rim. The percentage is the printed diameter against the 32.34 inches worked out above.
| Tire | Size as printed | Diameter | Width | Revs per mile |
|---|---|---|---|---|
| Toyo Open Country A/T III | P285/55R20 | 32.4 in (+0.2%) | 11.7 in | 642 |
| Toyo Open Country A/T III | LT285/55R20 | 32.4 in (+0.2%) | 11.7 in | 642 |
| Nitto Trail Grappler M/T | LT285/55R20 | 32.6 in (+0.8%) | 11.69 in | – |
Other 20-inch sizes against 285/55R20
Each size’s height against 285/55R20, and what a speedometer set for 285/55R20 shows at 60 mph with that size on.
| Size | Diameter | Width | Height change | At 60 mph shown |
|---|---|---|---|---|
| 245/50R20 | 29.6 in | 9.6 in | −8.3% | 55.0 mph |
| 255/50R20 | 30.0 in | 10.0 in | −7.1% | 55.7 mph |
| 255/55R20 | 31.0 in | 10.0 in | −4.0% | 57.6 mph |
| 275/55R20 compared | 31.9 in | 10.8 in | −1.3% | 59.2 mph |
| 275/60R20 | 33.0 in | 10.8 in | +2.0% | 61.2 mph |
| 275/65R20 | 34.1 in | 10.8 in | +5.4% | 63.2 mph |
| 285/60R20 compared | 33.5 in | 11.2 in | +3.5% | 62.1 mph |
| 33x12.50R20 | 33.0 in | 12.5 in | +2.0% | 61.2 mph |
| 35x12.50R20 | 35.0 in | 12.5 in | +8.2% | 64.9 mph |
285/55R20 compared
Every size: the tire size calculator. With the wheels off, the nuts go back on at your vehicle’s lug nut torque.
Questions
What is 285/55R20 in inches?
About 32.3x11.2R20: 32.3 inches tall and 11.2 inches wide on a 20-inch wheel, with 6.2-inch sidewalls. Exactly, 20 + 2 × 285 mm × 0.55 ÷ 25.4 = 32.34 inches.
How many revolutions per mile does a 285/55R20 make?
624 by its diameter: 63,360 inches in a mile ÷ 101.6 inches a turn. Tire makers’ published figures are measured under load, when the tire rolls on a slightly smaller radius, and run 2.8% to 3.3% higher in Toyo’s tables.
What flotation size is closest to 285/55R20?
Of the common 20-inch sizes, 33x12.50R20: 0.66 inches (17 mm) taller and 1.28 inches (32 mm) wider.
Is LT285/55R20 the same size as P285/55R20?
In dimensions, yes: the numbers mean the same in every metric size. The letters mark what the tire is built for, and an LT tire’s load is rated differently, so check the load index and pressure your vehicle needs before swapping one for the other.
Sources
- Bridgestone Americas: Determining tire size: P-metric, Euro-metric, LT-metric, C-type and flotation sizes, and what each number means (checked October 28, 2026)
- Toyo Tires: Extensa A/S II sizes and specifications: inflated overall diameter and width, revolutions per mile (checked October 28, 2026)
- Toyo Tires: Proxes Sport A/S sizes and specifications: inflated overall diameter and width, revolutions per mile (checked October 28, 2026)
- Toyo Tires: Open Country A/T III sizes and specifications: P-metric, LT-metric and flotation sizes, with revolutions per mile (checked October 28, 2026)
- Nitto Tire: Trail Grappler M/T sizes and specs: inflated overall diameter and width, LT-metric and flotation sizes (checked October 28, 2026)
Spotted a number that doesn’t match your manual or a source? Tell us; corrections are logged on the sources page.