275/55R20 vs 285/55R20 tire size
A 285/55R20 is 0.43 inches (11 mm) taller and 0.39 inches (10 mm) wider than a 275/55R20. Fit them in place of 275/55R20 tires and the speedometer reads low: at 60 mph on it you’re doing 60.8 mph, 1.4% faster, and the vehicle sits 0.22 inches (6 mm) higher.
Sources checked
| Dimension | 275/55R20 | 285/55R20 | Change |
|---|---|---|---|
| Overall diameter | 31.91 in (810 mm) | 32.34 in (822 mm) | +0.43 in (+12 mm) |
| Section width | 10.83 in (275 mm) | 11.22 in (285 mm) | +0.39 in (+10 mm) |
| Sidewall height | 5.95 in (151 mm) | 6.17 in (157 mm) | +0.22 in (+6 mm) |
| Aspect ratio | 55% | 55% | |
| Rim diameter | 20 in | 20 in | |
| Circumference | 100.2 in (2,546 mm) | 101.6 in (2,581 mm) | +1.4 in |
| Revolutions per mile | 632 | 624 | −8 |
| Revolutions per km | 393 | 387 | −6 |
Check another speed or size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
60.8mph
+1.4% · the speedometer reads low
- Height
- +0.43 in (+11 mm)
- Width
- +0.39 in (+10 mm)
- Ground clearance
- +0.22 in (+6 mm)
- Each side, same wheel
- +0.20 in (+5 mm)
275/55R20 and 285/55R20 side by side
| Dimension | 275/55R20 | 285/55R20 | Change |
|---|---|---|---|
| Overall diameter | 31.91 in (810 mm) | 32.34 in (822 mm) | +0.43 in (+12 mm) |
| Section width | 10.83 in (275 mm) | 11.22 in (285 mm) | +0.39 in (+10 mm) |
| Sidewall height | 5.95 in (151 mm) | 6.17 in (157 mm) | +0.22 in (+6 mm) |
| Aspect ratio | 55% | 55% | |
| Rim diameter | 20 in | 20 in | |
| Circumference | 100.2 in | 101.6 in | +1.4 in |
| Revolutions per mile | 632 | 624 | −8 |
| Revolutions per km | 393 | 387 | −6 |
The working
- 275/55R20: sidewall = 275 mm × 55% = 151.3 mm = 5.95 in.
- Diameter = rim + 2 × sidewall = 20 + 2 × 5.95 = 31.91 in (810 mm).
- Circumference = π × 31.91 = 100.2 in; revolutions per mile = 63,360 ÷ 100.2 = 632.
- 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.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 32.34 ÷ 31.91 = 60.8 mph.
- Ground clearance. Half the change in diameter: (32.34 − 31.91) ÷ 2 = +0.22 in.
Speedometer
A 285/55R20 turns 624 times a mile against the 275/55R20’s 632. With a speedometer set for 275/55R20, true speed is what it shows × 32.34 ÷ 31.91:
| Speedometer shows | True speed | Difference |
|---|---|---|
| 25 mph | 25.3 mph | +0.3 mph |
| 35 mph | 35.5 mph | +0.5 mph |
| 45 mph | 45.6 mph | +0.6 mph |
| 55 mph | 55.7 mph | +0.7 mph |
| 65 mph | 65.9 mph | +0.9 mph |
| 75 mph | 76.0 mph | +1.0 mph |
Clearance
- Ground clearance: +0.22 in (+6 mm), half the change in diameter.
- Top of the tread: +0.22 in (+6 mm), so that much less room under the fender.
- Each side, on the same wheel: +0.20 in (+5 mm), toward the suspension inside and toward the fender lip outside.
A new wheel with a different width or offset moves the tire again. The sidewall goes from 5.95 to 6.17 inches.
What tire makers publish
Inflated on the maker’s measuring rim; the percentage is against the arithmetic.
| Tire | Size as printed | Diameter | Width | Revs per mile |
|---|---|---|---|---|
| Toyo Open Country A/T III | 275/55R20 | 31.9 in (0.0%) | 11.2 in | 651 |
| Toyo Open Country A/T III | LT275/55R20 | 31.9 in (0.0%) | 11.2 in | 651 |
| 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 | – |
Each size on its own
- 275/55R20 tire size: 31.9 × 10.8 in
- 285/55R20 tire size: 32.3 × 11.2 in
Other comparisons
Questions
Can I fit 285/55R20 tires instead of 275/55R20?
They fit the same 20-inch wheels. A 285/55R20 is 0.43 inches (11 mm) taller and 0.39 inches (10 mm) wider than a 275/55R20, so check three things first: that your wheels are within the 285/55R20’s approved rim width range, which tire makers list for each size; that it clears the fenders and suspension at full lock and full travel; and that its load index meets what your door-jamb placard asks for.
How far off is the speedometer with 285/55R20 tires?
With a speedometer set for 275/55R20, the speedometer reads low: at 60 mph on it you’re doing 60.8 mph, 1.4% faster. The odometer is off the same way: over 1,000 miles driven it shows 986.6.
Does 285/55R20 change the ground clearance?
By +0.22 inches (+6 mm), half the change in diameter, at the axles and at the lowest point under them. On the same wheel, each sidewall sits 0.20 inches further out, inside and outside.
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.