-2.52%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 285/50R20, fitting 265/50R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.0 km/h | 25 mph | 24 mph |
| 60 km/h | 58.5 km/h | 37 mph | 36 mph |
| 80 km/h | 78.0 km/h | 50 mph | 48 mph |
| 100 km/h | 97.5 km/h | 62 mph | 61 mph |
| 120 km/h | 117.0 km/h | 75 mph | 73 mph |
Full comparison
285/50R20
Overall diameter793.0 mm · 31.22 in
Section width285 mm · 11.22 in
Sidewall height142.5 mm · 5.61 in
Circumference2491.3 mm · 98.1 in
Revolutions per mile646
Revolutions per km401
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
-2.52%Safe swap — speedometer error is minor
Original
Overall diameter793 mm · 31.22 in
Sidewall height142.5 mm
Circumference2,491.3 mm
Revolutions / mile646
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 -2.52%. 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 km/h | 25 mph | 24 mph |
| 60 km/h | 58.5 km/h | 37 mph | 36 mph |
| 80 km/h | 78 km/h | 50 mph | 48 mph |
| 100 km/h | 97.5 km/h | 62 mph | 61 mph |
| 120 km/h | 117 km/h | 75 mph | 73 mph |
See individual specs: 285/50R20 · 265/50R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.