-0.33%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 275/45R20, fitting 245/50R20 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 | 59.8 km/h | 37 mph | 37 mph |
| 80 km/h | 79.7 km/h | 50 mph | 50 mph |
| 100 km/h | 99.7 km/h | 62 mph | 62 mph |
| 120 km/h | 119.6 km/h | 75 mph | 74 mph |
Full comparison
275/45R20
Overall diameter755.5 mm · 29.74 in
Section width275 mm · 10.83 in
Sidewall height123.8 mm · 4.87 in
Circumference2373.5 mm · 93.4 in
Revolutions per mile678
Revolutions per km421
245/50R20
Overall diameter753.0 mm · 29.65 in
Section width245 mm · 9.65 in
Sidewall height122.5 mm · 4.82 in
Circumference2365.6 mm · 93.1 in
Revolutions per mile680
Revolutions per km423
-0.33%Safe swap — speedometer error is minor
Original
Overall diameter755.5 mm · 29.74 in
Sidewall height123.8 mm
Circumference2,373.5 mm
Revolutions / mile678.1
New
Overall diameter753 mm · 29.65 in
Sidewall height122.5 mm
Circumference2,365.6 mm
Revolutions / mile680.3
Speedometer & odometer error
The new tire changes overall diameter by -0.33%. 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 | 59.8 km/h | 37 mph | 37 mph |
| 80 km/h | 79.7 km/h | 50 mph | 50 mph |
| 100 km/h | 99.7 km/h | 62 mph | 62 mph |
| 120 km/h | 119.6 km/h | 75 mph | 74 mph |
See individual specs: 275/45R20 · 245/50R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.