-7.74%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 285/65R20, fitting 275/55R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 36.9 km/h | 25 mph | 23 mph |
| 60 km/h | 55.4 km/h | 37 mph | 34 mph |
| 80 km/h | 73.8 km/h | 50 mph | 46 mph |
| 100 km/h | 92.3 km/h | 62 mph | 57 mph |
| 120 km/h | 110.7 km/h | 75 mph | 69 mph |
Full comparison
285/65R20
Overall diameter878.5 mm · 34.59 in
Section width285 mm · 11.22 in
Sidewall height185.3 mm · 7.29 in
Circumference2759.9 mm · 108.7 in
Revolutions per mile583
Revolutions per km362
275/55R20
Overall diameter810.5 mm · 31.91 in
Section width275 mm · 10.83 in
Sidewall height151.3 mm · 5.95 in
Circumference2546.3 mm · 100.2 in
Revolutions per mile632
Revolutions per km393
-7.74%Not recommended — recalibrate the speedometer
Original
Overall diameter878.5 mm · 34.59 in
Sidewall height185.3 mm
Circumference2,759.9 mm
Revolutions / mile583.1
New
Overall diameter810.5 mm · 31.91 in
Sidewall height151.3 mm
Circumference2,546.3 mm
Revolutions / mile632
Speedometer & odometer error
The new tire changes overall diameter by -7.74%. 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 | 36.9 km/h | 25 mph | 23 mph |
| 60 km/h | 55.4 km/h | 37 mph | 34 mph |
| 80 km/h | 73.8 km/h | 50 mph | 46 mph |
| 100 km/h | 92.3 km/h | 62 mph | 57 mph |
| 120 km/h | 110.7 km/h | 75 mph | 69 mph |
See individual specs: 285/65R20 · 275/55R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.