235/60R18 vs 245/60R18 tire size
A 245/60R18 is 0.47 inches (12 mm) taller and 0.39 inches (10 mm) wider than a 235/60R18. Fit them in place of 235/60R18 tires and the speedometer reads low: at 60 mph on it you’re doing 61.0 mph, 1.6% faster, and the vehicle sits 0.24 inches (6 mm) higher.
Sources checked
| Dimension | 235/60R18 | 245/60R18 | Change |
|---|---|---|---|
| Overall diameter | 29.10 in (739 mm) | 29.57 in (751 mm) | +0.47 in (+12 mm) |
| Section width | 9.25 in (235 mm) | 9.65 in (245 mm) | +0.40 in (+10 mm) |
| Sidewall height | 5.55 in (141 mm) | 5.79 in (147 mm) | +0.24 in (+6 mm) |
| Aspect ratio | 60% | 60% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 91.4 in (2,322 mm) | 92.9 in (2,360 mm) | +1.5 in |
| Revolutions per mile | 693 | 682 | −11 |
| Revolutions per km | 431 | 424 | −7 |
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
- +0.47 in (+12 mm)
- Width
- +0.39 in (+10 mm)
- Ground clearance
- +0.24 in (+6 mm)
- Each side, same wheel
- +0.20 in (+5 mm)
235/60R18 and 245/60R18 side by side
| Dimension | 235/60R18 | 245/60R18 | Change |
|---|---|---|---|
| Overall diameter | 29.10 in (739 mm) | 29.57 in (751 mm) | +0.47 in (+12 mm) |
| Section width | 9.25 in (235 mm) | 9.65 in (245 mm) | +0.40 in (+10 mm) |
| Sidewall height | 5.55 in (141 mm) | 5.79 in (147 mm) | +0.24 in (+6 mm) |
| Aspect ratio | 60% | 60% | |
| Rim diameter | 18 in | 18 in | |
| Circumference | 91.4 in | 92.9 in | +1.5 in |
| Revolutions per mile | 693 | 682 | −11 |
| Revolutions per km | 431 | 424 | −7 |
The working
- 235/60R18: sidewall = 235 mm × 60% = 141.0 mm = 5.55 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 5.55 = 29.10 in (739 mm).
- Circumference = π × 29.10 = 91.4 in; revolutions per mile = 63,360 ÷ 91.4 = 693.
- 245/60R18: sidewall = 245 mm × 60% = 147.0 mm = 5.79 in.
- Diameter = rim + 2 × sidewall = 18 + 2 × 5.79 = 29.57 in (751 mm).
- Circumference = π × 29.57 = 92.9 in; revolutions per mile = 63,360 ÷ 92.9 = 682.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 29.57 ÷ 29.10 = 61.0 mph.
- Ground clearance. Half the change in diameter: (29.57 − 29.10) ÷ 2 = +0.24 in.
Speedometer
A 245/60R18 turns 682 times a mile against the 235/60R18’s 693. With a speedometer set for 235/60R18, true speed is what it shows × 29.57 ÷ 29.10:
| 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 | 66.1 mph | +1.1 mph |
| 75 mph | 76.2 mph | +1.2 mph |
Clearance
- Ground clearance: +0.24 in (+6 mm), half the change in diameter.
- Top of the tread: +0.24 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 5.55 to 5.79 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 | 235/60R18 | 29.1 in (0.0%) | 9.4 in | 714 |
| Toyo Open Country A/T III | 235/60R18 | 29.1 in (0.0%) | 9.4 in | 714 |
| Toyo Extensa A/S II | 245/60R18 | 29.6 in (+0.1%) | 9.8 in | 703 |
| Toyo Open Country A/T III | 245/60R18 | 29.6 in (+0.1%) | 9.8 in | 703 |
Each size on its own
- 235/60R18 tire size: 29.1 × 9.3 in
- 245/60R18 tire size: 29.6 × 9.6 in
Other comparisons
Questions
Can I fit 245/60R18 tires instead of 235/60R18?
They fit the same 18-inch wheels. A 245/60R18 is 0.47 inches (12 mm) taller and 0.39 inches (10 mm) wider than a 235/60R18, so check three things first: that your wheels are within the 245/60R18’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 245/60R18 tires?
With a speedometer set for 235/60R18, 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 984.0.
Does 245/60R18 change the ground clearance?
By +0.24 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.