+0.14%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 265/45R21, fitting 265/50R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.1 km/h | 25 mph | 25 mph |
| 60 km/h | 60.1 km/h | 37 mph | 37 mph |
| 80 km/h | 80.1 km/h | 50 mph | 50 mph |
| 100 km/h | 100.1 km/h | 62 mph | 62 mph |
| 120 km/h | 120.2 km/h | 75 mph | 75 mph |
Full comparison
265/45R21
Overall diameter771.9 mm · 30.39 in
Section width265 mm · 10.43 in
Sidewall height119.3 mm · 4.69 in
Circumference2425.0 mm · 95.5 in
Revolutions per mile664
Revolutions per km412
265/50R20
Overall diameter773.0 mm · 30.43 in
Section width265 mm · 10.43 in
Sidewall height132.5 mm · 5.22 in
Circumference2428.5 mm · 95.6 in
Revolutions per mile663
Revolutions per km412
+0.14%Safe swap — speedometer error is minor
Original
Overall diameter771.9 mm · 30.39 in
Sidewall height119.3 mm
Circumference2,425 mm
Revolutions / mile663.6
New
Overall diameter773 mm · 30.43 in
Sidewall height132.5 mm
Circumference2,428.5 mm
Revolutions / mile662.7
Speedometer & odometer error
The new tire changes overall diameter by +0.14%. 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 | 40.1 km/h | 25 mph | 25 mph |
| 60 km/h | 60.1 km/h | 37 mph | 37 mph |
| 80 km/h | 80.1 km/h | 50 mph | 50 mph |
| 100 km/h | 100.1 km/h | 62 mph | 62 mph |
| 120 km/h | 120.2 km/h | 75 mph | 75 mph |
See individual specs: 265/45R21 · 265/50R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.