QuickCheckToolsTire size calculator › 255/65R18 vs 275/65R18
255/65R18 vs 275/65R18
275/65R18 is 1.0 inches (3.3%) taller than 255/65R18 and 0.8 inches wider. Ground clearance changes by about 0.5 inches, and at an indicated 60 mph you would actually be doing 62.0 mph.
275/65R18 is 3.3% taller
That's more than the usual 3% guideline, so check clearance, and expect speedometer, ABS and gearing to be affected.
| 255/65R18 | 275/65R18 | Difference | |
|---|---|---|---|
| Overall diameter | 31.1 in | 32.1 in | +1.0 in |
| Width | 10.0 in | 10.8 in | +0.8 in |
| Sidewall height | 6.5 in | 7.0 in | +0.5 in |
| Circumference | 97.6 in | 100.8 in | +3.2 in |
| Revolutions per mile | 650 | 629 | -21 |
Speedometer with 275/65R18 fitted (calibrated for 255/65R18)
| Speedometer shows | Actual speed |
|---|---|
| 20 mph | 20.7 mph |
| 30 mph | 31.0 mph |
| 40 mph | 41.3 mph |
| 50 mph | 51.6 mph |
| 60 mph | 62.0 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.