-1.30%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 255/50R19, fitting 275/40R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.5 km/h | 25 mph | 25 mph |
| 60 km/h | 59.2 km/h | 37 mph | 37 mph |
| 80 km/h | 79.0 km/h | 50 mph | 49 mph |
| 100 km/h | 98.7 km/h | 62 mph | 61 mph |
| 120 km/h | 118.4 km/h | 75 mph | 74 mph |
Full comparison
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
275/40R20
Overall diameter728.0 mm · 28.66 in
Section width275 mm · 10.83 in
Sidewall height110.0 mm · 4.33 in
Circumference2287.1 mm · 90.0 in
Revolutions per mile704
Revolutions per km437
-1.3%Safe swap — speedometer error is minor
Original
Overall diameter737.6 mm · 29.04 in
Sidewall height127.5 mm
Circumference2,317.2 mm
Revolutions / mile694.5
New
Overall diameter728 mm · 28.66 in
Sidewall height110 mm
Circumference2,287.1 mm
Revolutions / mile703.7
Speedometer & odometer error
The new tire changes overall diameter by -1.3%. 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 | 39.5 km/h | 25 mph | 25 mph |
| 60 km/h | 59.2 km/h | 37 mph | 37 mph |
| 80 km/h | 79 km/h | 50 mph | 49 mph |
| 100 km/h | 98.7 km/h | 62 mph | 61 mph |
| 120 km/h | 118.4 km/h | 75 mph | 74 mph |
See individual specs: 255/50R19 · 275/40R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.