+0.94%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 235/35R19, fitting 245/40R18 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 | 80.8 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
235/35R19
Overall diameter647.1 mm · 25.48 in
Section width235 mm · 9.25 in
Sidewall height82.3 mm · 3.24 in
Circumference2032.9 mm · 80.0 in
Revolutions per mile792
Revolutions per km492
245/40R18
Overall diameter653.2 mm · 25.72 in
Section width245 mm · 9.65 in
Sidewall height98.0 mm · 3.86 in
Circumference2052.1 mm · 80.8 in
Revolutions per mile784
Revolutions per km487
+0.94%Safe swap — speedometer error is minor
Original
Overall diameter647.1 mm · 25.48 in
Sidewall height82.3 mm
Circumference2,032.9 mm
Revolutions / mile791.6
New
Overall diameter653.2 mm · 25.72 in
Sidewall height98 mm
Circumference2,052.1 mm
Revolutions / mile784.2
Speedometer & odometer error
The new tire changes overall diameter by +0.94%. 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 | 40.4 km/h | 25 mph | 25 mph |
| 60 km/h | 60.6 km/h | 37 mph | 38 mph |
| 80 km/h | 80.8 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: 235/35R19 · 245/40R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.