235/50R18 vs 235/55R18 tire size
A 235/55R18 is 0.93 inches (24 mm) taller than a 235/50R18, and the same width. Fit them in place of 235/50R18 tires and the speedometer reads low: at 60 mph on it you’re doing 62.0 mph, 3.4% faster, and the vehicle sits 0.46 inches (12 mm) higher.
Sources checked
| Dimension | 235/50R18 | 235/55R18 | Change |
|---|---|---|---|
| Overall diameter | 27.25 in (692 mm) | 28.18 in (716 mm) | +0.93 in (+24 mm) |
| Section width | 9.25 in (235 mm) | 9.25 in (235 mm) | 0.00 in (0 mm) |
| Sidewall height | 4.63 in (118 mm) | 5.09 in (129 mm) | +0.46 in (+11 mm) |
| Aspect ratio | 50% | 55% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 85.6 in (2,175 mm) | 88.5 in (2,248 mm) | +2.9 in |
| Revolutions per mile | 740 | 716 | −24 |
| Revolutions per km | 460 | 445 | −15 |
Check another speed or size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
62.0mph
+3.4% · the speedometer reads low
- Height
- +0.93 in (+24 mm)
- Width
- 0.00 in (0 mm)
- Ground clearance
- +0.46 in (+12 mm)
- Each side, same wheel
- 0.00 in (0 mm)
235/50R18 and 235/55R18 side by side
| Dimension | 235/50R18 | 235/55R18 | Change |
|---|---|---|---|
| Overall diameter | 27.25 in (692 mm) | 28.18 in (716 mm) | +0.93 in (+24 mm) |
| Section width | 9.25 in (235 mm) | 9.25 in (235 mm) | 0.00 in (0 mm) |
| Sidewall height | 4.63 in (118 mm) | 5.09 in (129 mm) | +0.46 in (+11 mm) |
| Aspect ratio | 50% | 55% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 85.6 in | 88.5 in | +2.9 in |
| Revolutions per mile | 740 | 716 | −24 |
| Revolutions per km | 460 | 445 | −15 |
The working
- 235/50R18: sidewall = 235 mm × 50% = 117.5 mm = 4.63 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 4.63 = 27.25 in (692 mm).
- Circumference = π × 27.25 = 85.6 in; revolutions per mile = 63,360 ÷ 85.6 = 740.
- 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 ÷ 27.25 = 62.0 mph.
- Ground clearance. Half the change in diameter: (28.18 − 27.25) ÷ 2 = +0.46 in.
Speedometer
A 235/55R18 turns 716 times a mile against the 235/50R18’s 740. With a speedometer set for 235/50R18, true speed is what it shows × 28.18 ÷ 27.25:
| Speedometer shows | True speed | Difference |
|---|---|---|
| 25 mph | 25.8 mph | +0.8 mph |
| 35 mph | 36.2 mph | +1.2 mph |
| 45 mph | 46.5 mph | +1.5 mph |
| 55 mph | 56.9 mph | +1.9 mph |
| 65 mph | 67.2 mph | +2.2 mph |
| 75 mph | 77.5 mph | +2.5 mph |
Clearance
- Ground clearance: +0.46 in (+12 mm), half the change in diameter.
- Top of the tread: +0.46 in (+12 mm), so that much less room under the fender.
- Each side, on the same wheel: no change.
A new wheel with a different width or offset moves the tire again. The sidewall goes from 4.63 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 | 235/50R18 | 27.3 in (+0.2%) | 9.6 in | 761 |
| 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
- 235/50R18 tire size: 27.3 × 9.3 in
- 235/55R18 tire size: 28.2 × 9.3 in
Other comparisons
Questions
Can I fit 235/55R18 tires instead of 235/50R18?
They fit the same 18-inch wheels. A 235/55R18 is 0.93 inches (24 mm) taller than a 235/50R18, and the same width, 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 235/50R18, the speedometer reads low: at 60 mph on it you’re doing 62.0 mph, 3.4% faster. The odometer is off the same way: over 1,000 miles driven it shows 967.2.
Does 235/55R18 change the ground clearance?
By +0.46 inches (+12 mm), half the change in diameter, at the axles and at the lowest point under them. The width doesn’t change.
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.