-4.65%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 285/60R20, fitting 275/55R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.1 km/h | 25 mph | 24 mph |
| 60 km/h | 57.2 km/h | 37 mph | 36 mph |
| 80 km/h | 76.3 km/h | 50 mph | 47 mph |
| 100 km/h | 95.4 km/h | 62 mph | 59 mph |
| 120 km/h | 114.4 km/h | 75 mph | 71 mph |
Full comparison
285/60R20
Overall diameter850.0 mm · 33.46 in
Section width285 mm · 11.22 in
Sidewall height171.0 mm · 6.73 in
Circumference2670.4 mm · 105.1 in
Revolutions per mile603
Revolutions per km374
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
-4.65%Borderline — noticeable speedometer/odometer error
Original
Overall diameter850 mm · 33.46 in
Sidewall height171 mm
Circumference2,670.4 mm
Revolutions / mile602.7
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 -4.65%. 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 | 38.1 km/h | 25 mph | 24 mph |
| 60 km/h | 57.2 km/h | 37 mph | 36 mph |
| 80 km/h | 76.3 km/h | 50 mph | 47 mph |
| 100 km/h | 95.4 km/h | 62 mph | 59 mph |
| 120 km/h | 114.4 km/h | 75 mph | 71 mph |
See individual specs: 285/60R20 · 275/55R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.