-5.08%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 275/65R20, fitting 285/55R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.0 km/h | 25 mph | 24 mph |
| 60 km/h | 56.9 km/h | 37 mph | 35 mph |
| 80 km/h | 75.9 km/h | 50 mph | 47 mph |
| 100 km/h | 94.9 km/h | 62 mph | 59 mph |
| 120 km/h | 113.9 km/h | 75 mph | 71 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
285/55R20
Overall diameter821.5 mm · 32.34 in
Section width285 mm · 11.22 in
Sidewall height156.8 mm · 6.17 in
Circumference2580.8 mm · 101.6 in
Revolutions per mile624
Revolutions per km387
-5.08%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 diameter821.5 mm · 32.34 in
Sidewall height156.8 mm
Circumference2,580.8 mm
Revolutions / mile623.6
Speedometer & odometer error
The new tire changes overall diameter by -5.08%. 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 | 38 km/h | 25 mph | 24 mph |
| 60 km/h | 56.9 km/h | 37 mph | 35 mph |
| 80 km/h | 75.9 km/h | 50 mph | 47 mph |
| 100 km/h | 94.9 km/h | 62 mph | 59 mph |
| 120 km/h | 113.9 km/h | 75 mph | 71 mph |
See individual specs: 275/65R20 · 285/55R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.