-0.24%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 225/55R17, fitting 245/45R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.9 km/h | 25 mph | 25 mph |
| 60 km/h | 59.9 km/h | 37 mph | 37 mph |
| 80 km/h | 79.8 km/h | 50 mph | 50 mph |
| 100 km/h | 99.8 km/h | 62 mph | 62 mph |
| 120 km/h | 119.7 km/h | 75 mph | 74 mph |
Full comparison
225/55R17
Overall diameter679.3 mm · 26.74 in
Section width225 mm · 8.86 in
Sidewall height123.8 mm · 4.87 in
Circumference2134.1 mm · 84.0 in
Revolutions per mile754
Revolutions per km469
245/45R18
Overall diameter677.7 mm · 26.68 in
Section width245 mm · 9.65 in
Sidewall height110.3 mm · 4.34 in
Circumference2129.1 mm · 83.8 in
Revolutions per mile756
Revolutions per km470
-0.24%Safe swap — speedometer error is minor
Original
Overall diameter679.3 mm · 26.74 in
Sidewall height123.8 mm
Circumference2,134.1 mm
Revolutions / mile754.1
New
Overall diameter677.7 mm · 26.68 in
Sidewall height110.3 mm
Circumference2,129.1 mm
Revolutions / mile755.9
Speedometer & odometer error
The new tire changes overall diameter by -0.24%. 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 | 39.9 km/h | 25 mph | 25 mph |
| 60 km/h | 59.9 km/h | 37 mph | 37 mph |
| 80 km/h | 79.8 km/h | 50 mph | 50 mph |
| 100 km/h | 99.8 km/h | 62 mph | 62 mph |
| 120 km/h | 119.7 km/h | 75 mph | 74 mph |
See individual specs: 225/55R17 · 245/45R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.