The new tire changes overall diameter by +4.94%. 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 | 42 km/h | 25 mph | 26 mph |
| 60 km/h | 63 km/h | 37 mph | 39 mph |
| 80 km/h | 84 km/h | 50 mph | 52 mph |
| 100 km/h | 104.9 km/h | 62 mph | 65 mph |
| 120 km/h | 125.9 km/h | 75 mph | 78 mph |
Commonly compared with 225/40R18
- 225/40R18 vs 205/50R17 · 205/50R17 specs
- 225/40R18 vs 225/45R17 · 225/45R17 specs
- 225/40R18 vs 265/30R19 · 265/30R19 specs
- 225/40R18 vs 235/45R17 · 235/45R17 specs
- 225/40R18 vs 235/40R18 · 235/40R18 specs
- 225/40R18 vs 215/50R17 · 215/50R17 specs
- 225/40R18 vs 235/35R19 · 235/35R19 specs
- 225/40R18 vs 215/45R17 · 215/45R17 specs
FAQ
What is the overall diameter of a 225/40R18 tire?
A 225/40R18 tire has an overall diameter of about 25.09 inches (637 mm) and a section width of 225 mm.
What sizes can replace a 225/40R18 tire?
Sizes within about ±3% of 225/40R18's 25.1-inch diameter are the closest matches, such as 205/50R17, 225/45R17, 265/30R19. 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.