225/55R18 vs 235/55R18 tire size
A 235/55R18 is 0.43 inches (11 mm) taller and 0.39 inches (10 mm) wider than a 225/55R18. Fit them in place of 225/55R18 tires and the speedometer reads low: at 60 mph on it you’re doing 60.9 mph, 1.6% faster, and the vehicle sits 0.22 inches (6 mm) higher.
Sources checked
| Dimension | 225/55R18 | 235/55R18 | Change |
|---|---|---|---|
| Overall diameter | 27.74 in (705 mm) | 28.18 in (716 mm) | +0.44 in (+11 mm) |
| Section width | 8.86 in (225 mm) | 9.25 in (235 mm) | +0.39 in (+10 mm) |
| Sidewall height | 4.87 in (124 mm) | 5.09 in (129 mm) | +0.22 in (+5 mm) |
| Aspect ratio | 55% | 55% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 87.2 in (2,214 mm) | 88.5 in (2,248 mm) | +1.3 in |
| Revolutions per mile | 727 | 716 | −11 |
| Revolutions per km | 452 | 445 | −7 |
Check another speed or size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
60.9mph
+1.6% · 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)
225/55R18 and 235/55R18 side by side
| Dimension | 225/55R18 | 235/55R18 | Change |
|---|---|---|---|
| Overall diameter | 27.74 in (705 mm) | 28.18 in (716 mm) | +0.44 in (+11 mm) |
| Section width | 8.86 in (225 mm) | 9.25 in (235 mm) | +0.39 in (+10 mm) |
| Sidewall height | 4.87 in (124 mm) | 5.09 in (129 mm) | +0.22 in (+5 mm) |
| Aspect ratio | 55% | 55% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 87.2 in | 88.5 in | +1.3 in |
| Revolutions per mile | 727 | 716 | −11 |
| Revolutions per km | 452 | 445 | −7 |
The working
- 225/55R18: sidewall = 225 mm × 55% = 123.8 mm = 4.87 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 4.87 = 27.74 in (705 mm).
- Circumference = π × 27.74 = 87.2 in; revolutions per mile = 63,360 ÷ 87.2 = 727.
- 235/55R18: sidewall = 235 mm × 55% = 129.3 mm = 5.09 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 5.09 = 28.18 in (716 mm).
- Circumference = π × 28.18 = 88.5 in; revolutions per mile = 63,360 ÷ 88.5 = 716.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 28.18 ÷ 27.74 = 60.9 mph.
- Ground clearance. Half the change in diameter: (28.18 − 27.74) ÷ 2 = +0.22 in.
Speedometer
A 235/55R18 turns 716 times a mile against the 225/55R18’s 727. With a speedometer set for 225/55R18, true speed is what it shows × 28.18 ÷ 27.74:
| Speedometer shows | True speed | Difference |
|---|---|---|
| 25 mph | 25.4 mph | +0.4 mph |
| 35 mph | 35.5 mph | +0.5 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: +0.22 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 4.87 to 5.09 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 Extensa A/S II | 225/55R18 | 27.8 in (+0.2%) | 9.2 in | 748 |
| Toyo Open Country A/T III | 225/55R18 | 27.8 in (+0.2%) | 9.2 in | 748 |
| Toyo Extensa A/S II | 235/55R18 | 28.1 in (−0.3%) | 9.6 in | 738 |
| Toyo Proxes Sport A/S | 235/55R18 | 28.1 in (−0.3%) | 9.6 in | 738 |
Each size on its own
- 225/55R18 tire size: 27.7 × 8.9 in
- 235/55R18 tire size: 28.2 × 9.3 in
Other comparisons
Questions
Can I fit 235/55R18 tires instead of 225/55R18?
They fit the same 18-inch wheels. A 235/55R18 is 0.43 inches (11 mm) taller and 0.39 inches (10 mm) wider than a 225/55R18, so check three things first: that your wheels are within the 235/55R18’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 235/55R18 tires?
With a speedometer set for 225/55R18, the speedometer reads low: at 60 mph on it you’re doing 60.9 mph, 1.6% faster. The odometer is off the same way: over 1,000 miles driven it shows 984.6.
Does 235/55R18 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.