+1.21%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 245/40R18, fitting 255/35R19 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.5 km/h | 25 mph | 25 mph |
| 60 km/h | 60.7 km/h | 37 mph | 38 mph |
| 80 km/h | 81.0 km/h | 50 mph | 50 mph |
| 100 km/h | 101.2 km/h | 62 mph | 63 mph |
| 120 km/h | 121.5 km/h | 75 mph | 75 mph |
Full comparison
245/40R18
Overall diameter653.2 mm · 25.72 in
Section width245 mm · 9.65 in
Sidewall height98.0 mm · 3.86 in
Circumference2052.1 mm · 80.8 in
Revolutions per mile784
Revolutions per km487
255/35R19
Overall diameter661.1 mm · 26.03 in
Section width255 mm · 10.04 in
Sidewall height89.3 mm · 3.51 in
Circumference2076.9 mm · 81.8 in
Revolutions per mile775
Revolutions per km481
+1.21%Safe swap — speedometer error is minor
Original
Overall diameter653.2 mm · 25.72 in
Sidewall height98 mm
Circumference2,052.1 mm
Revolutions / mile784.2
New
Overall diameter661.1 mm · 26.03 in
Sidewall height89.3 mm
Circumference2,076.9 mm
Revolutions / mile774.9
Speedometer & odometer error
The new tire changes overall diameter by +1.21%. 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 | 40.5 km/h | 25 mph | 25 mph |
| 60 km/h | 60.7 km/h | 37 mph | 38 mph |
| 80 km/h | 81 km/h | 50 mph | 50 mph |
| 100 km/h | 101.2 km/h | 62 mph | 63 mph |
| 120 km/h | 121.5 km/h | 75 mph | 75 mph |
See individual specs: 245/40R18 · 255/35R19. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.