-0.07%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 245/45R20, fitting 275/40R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.0 km/h | 25 mph | 25 mph |
| 60 km/h | 60.0 km/h | 37 mph | 37 mph |
| 80 km/h | 79.9 km/h | 50 mph | 50 mph |
| 100 km/h | 99.9 km/h | 62 mph | 62 mph |
| 120 km/h | 119.9 km/h | 75 mph | 75 mph |
Full comparison
245/45R20
Overall diameter728.5 mm · 28.68 in
Section width245 mm · 9.65 in
Sidewall height110.3 mm · 4.34 in
Circumference2288.7 mm · 90.1 in
Revolutions per mile703
Revolutions per km437
275/40R20
Overall diameter728.0 mm · 28.66 in
Section width275 mm · 10.83 in
Sidewall height110.0 mm · 4.33 in
Circumference2287.1 mm · 90.0 in
Revolutions per mile704
Revolutions per km437
-0.07%Safe swap — speedometer error is minor
Original
Overall diameter728.5 mm · 28.68 in
Sidewall height110.3 mm
Circumference2,288.7 mm
Revolutions / mile703.2
New
Overall diameter728 mm · 28.66 in
Sidewall height110 mm
Circumference2,287.1 mm
Revolutions / mile703.7
Speedometer & odometer error
The new tire changes overall diameter by -0.07%. 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 km/h | 25 mph | 25 mph |
| 60 km/h | 60 km/h | 37 mph | 37 mph |
| 80 km/h | 79.9 km/h | 50 mph | 50 mph |
| 100 km/h | 99.9 km/h | 62 mph | 62 mph |
| 120 km/h | 119.9 km/h | 75 mph | 75 mph |
See individual specs: 245/45R20 · 275/40R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.