-1.43%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 255/50R20, fitting 245/55R19 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.4 km/h | 25 mph | 24 mph |
| 60 km/h | 59.1 km/h | 37 mph | 37 mph |
| 80 km/h | 78.9 km/h | 50 mph | 49 mph |
| 100 km/h | 98.6 km/h | 62 mph | 61 mph |
| 120 km/h | 118.3 km/h | 75 mph | 73 mph |
Full comparison
255/50R20
Overall diameter763.0 mm · 30.04 in
Section width255 mm · 10.04 in
Sidewall height127.5 mm · 5.02 in
Circumference2397.0 mm · 94.4 in
Revolutions per mile671
Revolutions per km417
245/55R19
Overall diameter752.1 mm · 29.61 in
Section width245 mm · 9.65 in
Sidewall height134.8 mm · 5.31 in
Circumference2362.8 mm · 93.0 in
Revolutions per mile681
Revolutions per km423
-1.43%Safe swap — speedometer error is minor
Original
Overall diameter763 mm · 30.04 in
Sidewall height127.5 mm
Circumference2,397 mm
Revolutions / mile671.4
New
Overall diameter752.1 mm · 29.61 in
Sidewall height134.8 mm
Circumference2,362.8 mm
Revolutions / mile681.1
Speedometer & odometer error
The new tire changes overall diameter by -1.43%. 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 | 39.4 km/h | 25 mph | 24 mph |
| 60 km/h | 59.1 km/h | 37 mph | 37 mph |
| 80 km/h | 78.9 km/h | 50 mph | 49 mph |
| 100 km/h | 98.6 km/h | 62 mph | 61 mph |
| 120 km/h | 118.3 km/h | 75 mph | 73 mph |
See individual specs: 255/50R20 · 245/55R19. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.