The new tire changes overall diameter by -9.35%. With a speedometer calibrated to the original tire, that same percentage is how far the speedometer and odometer read off — a taller tire means your true speed is higher than indicated and the odometer under-counts distance.
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 36.3 km/h | 25 mph | 23 mph |
| 60 km/h | 54.4 km/h | 37 mph | 34 mph |
| 80 km/h | 72.5 km/h | 50 mph | 45 mph |
| 100 km/h | 90.6 km/h | 62 mph | 56 mph |
| 120 km/h | 108.8 km/h | 75 mph | 68 mph |
Commonly compared with 255/55R18
- 255/55R18 vs 255/50R19 · 255/50R19 specs
- 255/55R18 vs 235/65R17 · 235/65R17 specs
- 255/55R18 vs 285/45R19 · 285/45R19 specs
- 255/55R18 vs 235/60R18 · 235/60R18 specs
- 255/55R18 vs 235/55R19 · 235/55R19 specs
- 255/55R18 vs 265/50R19 · 265/50R19 specs
- 255/55R18 vs 245/65R17 · 245/65R17 specs
- 255/55R18 vs 225/65R17 · 225/65R17 specs
FAQ
What is the overall diameter of a 255/55R18 tire?
A 255/55R18 tire has an overall diameter of about 29.04 inches (738 mm) and a section width of 255 mm.
What sizes can replace a 255/55R18 tire?
Sizes within about ±3% of 255/55R18's 29.0-inch diameter are the closest matches, such as 255/50R19, 235/65R17, 285/45R19. Use the calculator above to check the exact speedometer effect of any substitute.
Fitment & trouble codes
Changing tire size by more than about 3% shifts the speedometer, odometer and, on some vehicles, ABS/traction calibration — which can set wheel-speed-sensor or vehicle-speed codes. See C1234 (wheel speed sensor) and C0050 (rear wheel speed) if a warning light appears after a size change.