+0.22%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 255/45R20, fitting 285/45R19 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.1 km/h | 25 mph | 25 mph |
| 60 km/h | 60.1 km/h | 37 mph | 37 mph |
| 80 km/h | 80.2 km/h | 50 mph | 50 mph |
| 100 km/h | 100.2 km/h | 62 mph | 62 mph |
| 120 km/h | 120.3 km/h | 75 mph | 75 mph |
Full comparison
255/45R20
Overall diameter737.5 mm · 29.04 in
Section width255 mm · 10.04 in
Sidewall height114.8 mm · 4.52 in
Circumference2316.9 mm · 91.2 in
Revolutions per mile695
Revolutions per km432
285/45R19
Overall diameter739.1 mm · 29.10 in
Section width285 mm · 11.22 in
Sidewall height128.3 mm · 5.05 in
Circumference2322.0 mm · 91.4 in
Revolutions per mile693
Revolutions per km431
+0.22%Safe swap — speedometer error is minor
Original
Overall diameter737.5 mm · 29.04 in
Sidewall height114.8 mm
Circumference2,316.9 mm
Revolutions / mile694.6
New
Overall diameter739.1 mm · 29.1 in
Sidewall height128.3 mm
Circumference2,322 mm
Revolutions / mile693.1
Speedometer & odometer error
The new tire changes overall diameter by +0.22%. 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 | 40.1 km/h | 25 mph | 25 mph |
| 60 km/h | 60.1 km/h | 37 mph | 37 mph |
| 80 km/h | 80.2 km/h | 50 mph | 50 mph |
| 100 km/h | 100.2 km/h | 62 mph | 62 mph |
| 120 km/h | 120.3 km/h | 75 mph | 75 mph |
See individual specs: 255/45R20 · 285/45R19. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.