-8.38%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 275/65R20, fitting 285/50R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 36.6 km/h | 25 mph | 23 mph |
| 60 km/h | 55.0 km/h | 37 mph | 34 mph |
| 80 km/h | 73.3 km/h | 50 mph | 46 mph |
| 100 km/h | 91.6 km/h | 62 mph | 57 mph |
| 120 km/h | 109.9 km/h | 75 mph | 68 mph |
Full comparison
275/65R20
Overall diameter865.5 mm · 34.07 in
Section width275 mm · 10.83 in
Sidewall height178.8 mm · 7.04 in
Circumference2719.0 mm · 107.0 in
Revolutions per mile592
Revolutions per km368
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
-8.38%Not recommended — recalibrate the speedometer
Original
Overall diameter865.5 mm · 34.07 in
Sidewall height178.8 mm
Circumference2,719 mm
Revolutions / mile591.9
New
Overall diameter793 mm · 31.22 in
Sidewall height142.5 mm
Circumference2,491.3 mm
Revolutions / mile646
Speedometer & odometer error
The new tire changes overall diameter by -8.38%. 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 | 36.6 km/h | 25 mph | 23 mph |
| 60 km/h | 55 km/h | 37 mph | 34 mph |
| 80 km/h | 73.3 km/h | 50 mph | 46 mph |
| 100 km/h | 91.6 km/h | 62 mph | 57 mph |
| 120 km/h | 109.9 km/h | 75 mph | 68 mph |
See individual specs: 275/65R20 · 285/50R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.