+0.92%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 225/40R19, fitting 235/45R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.4 km/h | 25 mph | 25 mph |
| 60 km/h | 60.6 km/h | 37 mph | 38 mph |
| 80 km/h | 80.7 km/h | 50 mph | 50 mph |
| 100 km/h | 100.9 km/h | 62 mph | 63 mph |
| 120 km/h | 121.1 km/h | 75 mph | 75 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
235/45R18
Overall diameter668.7 mm · 26.33 in
Section width235 mm · 9.25 in
Sidewall height105.8 mm · 4.16 in
Circumference2100.8 mm · 82.7 in
Revolutions per mile766
Revolutions per km476
+0.92%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 diameter668.7 mm · 26.33 in
Sidewall height105.8 mm
Circumference2,100.8 mm
Revolutions / mile766.1
Speedometer & odometer error
The new tire changes overall diameter by +0.92%. 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 | 40.4 km/h | 25 mph | 25 mph |
| 60 km/h | 60.6 km/h | 37 mph | 38 mph |
| 80 km/h | 80.7 km/h | 50 mph | 50 mph |
| 100 km/h | 100.9 km/h | 62 mph | 63 mph |
| 120 km/h | 121.1 km/h | 75 mph | 75 mph |
See individual specs: 225/40R19 · 235/45R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.