+1.81%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 265/30R19, fitting 245/40R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.7 km/h | 25 mph | 25 mph |
| 60 km/h | 61.1 km/h | 37 mph | 38 mph |
| 80 km/h | 81.4 km/h | 50 mph | 51 mph |
| 100 km/h | 101.8 km/h | 62 mph | 63 mph |
| 120 km/h | 122.2 km/h | 75 mph | 76 mph |
Full comparison
265/30R19
Overall diameter641.6 mm · 25.26 in
Section width265 mm · 10.43 in
Sidewall height79.5 mm · 3.13 in
Circumference2015.6 mm · 79.4 in
Revolutions per mile798
Revolutions per km496
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
+1.81%Safe swap — speedometer error is minor
Original
Overall diameter641.6 mm · 25.26 in
Sidewall height79.5 mm
Circumference2,015.6 mm
Revolutions / mile798.4
New
Overall diameter653.2 mm · 25.72 in
Sidewall height98 mm
Circumference2,052.1 mm
Revolutions / mile784.2
Speedometer & odometer error
The new tire changes overall diameter by +1.81%. 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 | 40.7 km/h | 25 mph | 25 mph |
| 60 km/h | 61.1 km/h | 37 mph | 38 mph |
| 80 km/h | 81.4 km/h | 50 mph | 51 mph |
| 100 km/h | 101.8 km/h | 62 mph | 63 mph |
| 120 km/h | 122.2 km/h | 75 mph | 76 mph |
See individual specs: 265/30R19 · 245/40R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.