+2.28%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 225/40R19, fitting 245/45R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.9 km/h | 25 mph | 25 mph |
| 60 km/h | 61.4 km/h | 37 mph | 38 mph |
| 80 km/h | 81.8 km/h | 50 mph | 51 mph |
| 100 km/h | 102.3 km/h | 62 mph | 64 mph |
| 120 km/h | 122.7 km/h | 75 mph | 76 mph |
Full comparison
225/40R19
Overall diameter662.6 mm · 26.09 in
Section width225 mm · 8.86 in
Sidewall height90.0 mm · 3.54 in
Circumference2081.6 mm · 82.0 in
Revolutions per mile773
Revolutions per km480
245/45R18
Overall diameter677.7 mm · 26.68 in
Section width245 mm · 9.65 in
Sidewall height110.3 mm · 4.34 in
Circumference2129.1 mm · 83.8 in
Revolutions per mile756
Revolutions per km470
+2.28%Safe swap — speedometer error is minor
Original
Overall diameter662.6 mm · 26.09 in
Sidewall height90 mm
Circumference2,081.6 mm
Revolutions / mile773.1
New
Overall diameter677.7 mm · 26.68 in
Sidewall height110.3 mm
Circumference2,129.1 mm
Revolutions / mile755.9
Speedometer & odometer error
The new tire changes overall diameter by +2.28%. 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 | 40.9 km/h | 25 mph | 25 mph |
| 60 km/h | 61.4 km/h | 37 mph | 38 mph |
| 80 km/h | 81.8 km/h | 50 mph | 51 mph |
| 100 km/h | 102.3 km/h | 62 mph | 64 mph |
| 120 km/h | 122.7 km/h | 75 mph | 76 mph |
See individual specs: 225/40R19 · 245/45R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.