QuickCheckToolsTire size calculator › 255/70R17 vs 255/75R17
255/70R17 vs 255/75R17
255/75R17 is 1.0 inches (3.2%) taller than 255/70R17 and the same width. Ground clearance changes by about 0.5 inches, and at an indicated 60 mph you would actually be doing 61.9 mph.
255/75R17 is 3.2% taller
That's more than the usual 3% guideline, so check clearance, and expect speedometer, ABS and gearing to be affected.
| 255/70R17 | 255/75R17 | Difference | |
|---|---|---|---|
| Overall diameter | 31.1 in | 32.1 in | +1.0 in |
| Width | 10.0 in | 10.0 in | 0.0 in |
| Sidewall height | 7.0 in | 7.5 in | +0.5 in |
| Circumference | 97.6 in | 100.7 in | +3.2 in |
| Revolutions per mile | 649 | 629 | -20 |
Speedometer with 255/75R17 fitted (calibrated for 255/70R17)
| Speedometer shows | Actual speed |
|---|---|
| 20 mph | 20.6 mph |
| 30 mph | 31.0 mph |
| 40 mph | 41.3 mph |
| 50 mph | 51.6 mph |
| 60 mph | 61.9 mph |
| 70 mph | 72.3 mph |
| 80 mph | 82.6 mph |
Open this comparison in the calculator
What the difference means
Diameter is what matters most. A taller tire raises the vehicle by half the difference, here about 0.5 inches, and covers more ground per turn, so the speedometer reads lower than your real speed. Width changes how much tread meets the road and whether the tire clears suspension parts and wheel arches.
These are design dimensions calculated from the sizes. Actual tires vary slightly by brand and model, so check fitment for your vehicle before buying.