-0.81%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 235/50R18, fitting 255/40R19 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.7 km/h | 25 mph | 25 mph |
| 60 km/h | 59.5 km/h | 37 mph | 37 mph |
| 80 km/h | 79.4 km/h | 50 mph | 49 mph |
| 100 km/h | 99.2 km/h | 62 mph | 62 mph |
| 120 km/h | 119.0 km/h | 75 mph | 74 mph |
Full comparison
235/50R18
Overall diameter692.2 mm · 27.25 in
Section width235 mm · 9.25 in
Sidewall height117.5 mm · 4.63 in
Circumference2174.6 mm · 85.6 in
Revolutions per mile740
Revolutions per km460
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
-0.81%Safe swap — speedometer error is minor
Original
Overall diameter692.2 mm · 27.25 in
Sidewall height117.5 mm
Circumference2,174.6 mm
Revolutions / mile740.1
New
Overall diameter686.6 mm · 27.03 in
Sidewall height102 mm
Circumference2,157 mm
Revolutions / mile746.1
Speedometer & odometer error
The new tire changes overall diameter by -0.81%. 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 | 39.7 km/h | 25 mph | 25 mph |
| 60 km/h | 59.5 km/h | 37 mph | 37 mph |
| 80 km/h | 79.4 km/h | 50 mph | 49 mph |
| 100 km/h | 99.2 km/h | 62 mph | 62 mph |
| 120 km/h | 119 km/h | 75 mph | 74 mph |
See individual specs: 235/50R18 · 255/40R19. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.