-1.17%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 255/40R19, fitting 245/40R19 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 | 59.3 km/h | 37 mph | 37 mph |
| 80 km/h | 79.1 km/h | 50 mph | 49 mph |
| 100 km/h | 98.8 km/h | 62 mph | 61 mph |
| 120 km/h | 118.6 km/h | 75 mph | 74 mph |
Full comparison
255/40R19
Overall diameter686.6 mm · 27.03 in
Section width255 mm · 10.04 in
Sidewall height102.0 mm · 4.02 in
Circumference2157.0 mm · 84.9 in
Revolutions per mile746
Revolutions per km464
245/40R19
Overall diameter678.6 mm · 26.72 in
Section width245 mm · 9.65 in
Sidewall height98.0 mm · 3.86 in
Circumference2131.9 mm · 83.9 in
Revolutions per mile755
Revolutions per km469
-1.17%Safe swap — speedometer error is minor
Original
Overall diameter686.6 mm · 27.03 in
Sidewall height102 mm
Circumference2,157 mm
Revolutions / mile746.1
New
Overall diameter678.6 mm · 26.72 in
Sidewall height98 mm
Circumference2,131.9 mm
Revolutions / mile754.9
Speedometer & odometer error
The new tire changes overall diameter by -1.17%. 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 | 59.3 km/h | 37 mph | 37 mph |
| 80 km/h | 79.1 km/h | 50 mph | 49 mph |
| 100 km/h | 98.8 km/h | 62 mph | 61 mph |
| 120 km/h | 118.6 km/h | 75 mph | 74 mph |
See individual specs: 255/40R19 · 245/40R19. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.