245/70R17 vs 255/70R17 tire size
A 255/70R17 is 0.55 inches (14 mm) taller and 0.39 inches (10 mm) wider than a 245/70R17. Fit them in place of 245/70R17 tires and the speedometer reads low: at 60 mph on it you’re doing 61.1 mph, 1.8% faster, and the vehicle sits 0.28 inches (7 mm) higher.
Sources checked
| Dimension | 245/70R17 | 255/70R17 | Change |
|---|---|---|---|
| Overall diameter | 30.50 in (775 mm) | 31.06 in (789 mm) | +0.56 in (+14 mm) |
| Section width | 9.65 in (245 mm) | 10.04 in (255 mm) | +0.39 in (+10 mm) |
| Sidewall height | 6.75 in (172 mm) | 7.03 in (179 mm) | +0.28 in (+7 mm) |
| Aspect ratio | 70% | 70% | |
| Rim diameter | 17 in | 17 in | |
| Circumference | 95.8 in (2,434 mm) | 97.6 in (2,478 mm) | +1.8 in |
| Revolutions per mile | 661 | 649 | −12 |
| Revolutions per km | 411 | 404 | −7 |
Check another speed or size
Metric, LT and flotation
At 60 mph on the speedometer you’re doing
61.1mph
+1.8% · the speedometer reads low
- Height
- +0.55 in (+14 mm)
- Width
- +0.39 in (+10 mm)
- Ground clearance
- +0.28 in (+7 mm)
- Each side, same wheel
- +0.20 in (+5 mm)
245/70R17 and 255/70R17 side by side
| Dimension | 245/70R17 | 255/70R17 | Change |
|---|---|---|---|
| Overall diameter | 30.50 in (775 mm) | 31.06 in (789 mm) | +0.56 in (+14 mm) |
| Section width | 9.65 in (245 mm) | 10.04 in (255 mm) | +0.39 in (+10 mm) |
| Sidewall height | 6.75 in (172 mm) | 7.03 in (179 mm) | +0.28 in (+7 mm) |
| Aspect ratio | 70% | 70% | |
| Rim diameter | 17 in | 17 in | |
| Circumference | 95.8 in | 97.6 in | +1.8 in |
| Revolutions per mile | 661 | 649 | −12 |
| Revolutions per km | 411 | 404 | −7 |
The working
- 245/70R17: sidewall = 245 mm × 70% = 171.5 mm = 6.75 in.
- Diameter = rim + 2 × sidewall = 17 + 2 × 6.75 = 30.50 in (775 mm).
- Circumference = π × 30.50 = 95.8 in; revolutions per mile = 63,360 ÷ 95.8 = 661.
- 255/70R17: sidewall = 255 mm × 70% = 178.5 mm = 7.03 in.
- Diameter = rim + 2 × sidewall = 17 + 2 × 7.03 = 31.06 in (789 mm).
- Circumference = π × 31.06 = 97.6 in; revolutions per mile = 63,360 ÷ 97.6 = 649.
- Speedometer. True speed = what it shows × new diameter ÷ old = 60 × 31.06 ÷ 30.50 = 61.1 mph.
- Ground clearance. Half the change in diameter: (31.06 − 30.50) ÷ 2 = +0.28 in.
Speedometer
A 255/70R17 turns 649 times a mile against the 245/70R17’s 661. With a speedometer set for 245/70R17, true speed is what it shows × 31.06 ÷ 30.50:
| Speedometer shows | True speed | Difference |
|---|---|---|
| 25 mph | 25.5 mph | +0.5 mph |
| 35 mph | 35.6 mph | +0.6 mph |
| 45 mph | 45.8 mph | +0.8 mph |
| 55 mph | 56.0 mph | +1.0 mph |
| 65 mph | 66.2 mph | +1.2 mph |
| 75 mph | 76.4 mph | +1.4 mph |
Clearance
- Ground clearance: +0.28 in (+7 mm), half the change in diameter.
- Top of the tread: +0.28 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 6.75 to 7.03 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 | 245/70R17 | 30.6 in (+0.3%) | 9.8 in | 680 |
| Toyo Open Country A/T III | LT245/70R17 | 30.6 in (+0.3%) | 9.8 in | 680 |
| Toyo Open Country A/T III | 255/70R17 | 31.1 in (+0.1%) | 10.2 in | 668 |
| Toyo Open Country A/T III | LT255/70R17 | 31.1 in (+0.1%) | 10.2 in | 668 |
Each size on its own
- 245/70R17 tire size: 30.5 × 9.6 in
- 255/70R17 tire size: 31.1 × 10.0 in
Other comparisons
Questions
Can I fit 255/70R17 tires instead of 245/70R17?
They fit the same 17-inch wheels. A 255/70R17 is 0.55 inches (14 mm) taller and 0.39 inches (10 mm) wider than a 245/70R17, so check three things first: that your wheels are within the 255/70R17’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 255/70R17 tires?
With a speedometer set for 245/70R17, the speedometer reads low: at 60 mph on it you’re doing 61.1 mph, 1.8% faster. The odometer is off the same way: over 1,000 miles driven it shows 982.3.
Does 255/70R17 change the ground clearance?
By +0.28 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.