275/65R18 vs 285/65R18 tire size
A 285/65R18 is 0.51 inches (13 mm) taller and 0.39 inches (10 mm) wider than a 275/65R18. Fit them in place of 275/65R18 tires and the speedometer reads low: at 60 mph on it you’re doing 61.0 mph, 1.6% faster, and the vehicle sits 0.26 inches (7 mm) higher.
Sources checked
| Dimension | 275/65R18 | 285/65R18 | Change |
|---|---|---|---|
| Overall diameter | 32.07 in (815 mm) | 32.59 in (828 mm) | +0.52 in (+13 mm) |
| Section width | 10.83 in (275 mm) | 11.22 in (285 mm) | +0.39 in (+10 mm) |
| Sidewall height | 7.04 in (179 mm) | 7.29 in (185 mm) | +0.25 in (+6 mm) |
| Aspect ratio | 65% | 65% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 100.8 in (2,559 mm) | 102.4 in (2,600 mm) | +1.6 in |
| Revolutions per mile | 629 | 619 | −10 |
| Revolutions per km | 391 | 385 | −6 |
Check another speed or size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
61.0mph
+1.6% · the speedometer reads low
- Height
- +0.51 in (+13 mm)
- Width
- +0.39 in (+10 mm)
- Ground clearance
- +0.26 in (+7 mm)
- Each side, same wheel
- +0.20 in (+5 mm)
275/65R18 and 285/65R18 side by side
| Dimension | 275/65R18 | 285/65R18 | Change |
|---|---|---|---|
| Overall diameter | 32.07 in (815 mm) | 32.59 in (828 mm) | +0.52 in (+13 mm) |
| Section width | 10.83 in (275 mm) | 11.22 in (285 mm) | +0.39 in (+10 mm) |
| Sidewall height | 7.04 in (179 mm) | 7.29 in (185 mm) | +0.25 in (+6 mm) |
| Aspect ratio | 65% | 65% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 100.8 in | 102.4 in | +1.6 in |
| Revolutions per mile | 629 | 619 | −10 |
| Revolutions per km | 391 | 385 | −6 |
The working
- 275/65R18: sidewall = 275 mm × 65% = 178.8 mm = 7.04 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 7.04 = 32.07 in (815 mm).
- Circumference = π × 32.07 = 100.8 in; revolutions per mile = 63,360 ÷ 100.8 = 629.
- 285/65R18: sidewall = 285 mm × 65% = 185.3 mm = 7.29 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 7.29 = 32.59 in (828 mm).
- Circumference = π × 32.59 = 102.4 in; revolutions per mile = 63,360 ÷ 102.4 = 619.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 32.59 ÷ 32.07 = 61.0 mph.
- Ground clearance. Half the change in diameter: (32.59 − 32.07) ÷ 2 = +0.26 in.
Speedometer
A 285/65R18 turns 619 times a mile against the 275/65R18’s 629. With a speedometer set for 275/65R18, true speed is what it shows × 32.59 ÷ 32.07:
| Speedometer shows | True speed | Difference |
|---|---|---|
| 25 mph | 25.4 mph | +0.4 mph |
| 35 mph | 35.6 mph | +0.6 mph |
| 45 mph | 45.7 mph | +0.7 mph |
| 55 mph | 55.9 mph | +0.9 mph |
| 65 mph | 66.0 mph | +1.0 mph |
| 75 mph | 76.2 mph | +1.2 mph |
Clearance
- Ground clearance: +0.26 in (+7 mm), half the change in diameter.
- Top of the tread: +0.26 in (+7 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 7.04 to 7.29 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 | 275/65R18 | 32.1 in (+0.1%) | 11 in | 647 |
| Toyo Open Country A/T III, outlined white letters | LT275/65R18 | 32.3 in (+0.7%) | 11 in | 643 |
| Toyo Open Country A/T III, black sidewall | LT275/65R18 | 32.1 in (+0.1%) | 11 in | 647 |
| Toyo Open Country A/T III | LT285/65R18 | 32.6 in (0.0%) | 11.5 in | 638 |
| Nitto Trail Grappler M/T | LT285/65R18 | 32.83 in (+0.7%) | 11.93 in | – |
Each size on its own
- 275/65R18 tire size: 32.1 × 10.8 in
- 285/65R18 tire size: 32.6 × 11.2 in
Other comparisons
Questions
Can I fit 285/65R18 tires instead of 275/65R18?
They fit the same 18-inch wheels. A 285/65R18 is 0.51 inches (13 mm) taller and 0.39 inches (10 mm) wider than a 275/65R18, so check three things first: that your wheels are within the 285/65R18’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 285/65R18 tires?
With a speedometer set for 275/65R18, the speedometer reads low: at 60 mph on it you’re doing 61.0 mph, 1.6% faster. The odometer is off the same way: over 1,000 miles driven it shows 984.3.
Does 285/65R18 change the ground clearance?
By +0.26 inches (+7 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.