+1.25%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 245/45R20, fitting 255/50R19 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.5 km/h | 25 mph | 25 mph |
| 60 km/h | 60.7 km/h | 37 mph | 38 mph |
| 80 km/h | 81.0 km/h | 50 mph | 50 mph |
| 100 km/h | 101.2 km/h | 62 mph | 63 mph |
| 120 km/h | 121.5 km/h | 75 mph | 75 mph |
Full comparison
245/45R20
Overall diameter728.5 mm · 28.68 in
Section width245 mm · 9.65 in
Sidewall height110.3 mm · 4.34 in
Circumference2288.7 mm · 90.1 in
Revolutions per mile703
Revolutions per km437
255/50R19
Overall diameter737.6 mm · 29.04 in
Section width255 mm · 10.04 in
Sidewall height127.5 mm · 5.02 in
Circumference2317.2 mm · 91.2 in
Revolutions per mile695
Revolutions per km432
+1.25%Safe swap — speedometer error is minor
Original
Overall diameter728.5 mm · 28.68 in
Sidewall height110.3 mm
Circumference2,288.7 mm
Revolutions / mile703.2
New
Overall diameter737.6 mm · 29.04 in
Sidewall height127.5 mm
Circumference2,317.2 mm
Revolutions / mile694.5
Speedometer & odometer error
The new tire changes overall diameter by +1.25%. 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 | 40.5 km/h | 25 mph | 25 mph |
| 60 km/h | 60.7 km/h | 37 mph | 38 mph |
| 80 km/h | 81 km/h | 50 mph | 50 mph |
| 100 km/h | 101.2 km/h | 62 mph | 63 mph |
| 120 km/h | 121.5 km/h | 75 mph | 75 mph |
See individual specs: 245/45R20 · 255/50R19. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.