-6.35%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 275/65R20, fitting 275/55R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 37.5 km/h | 25 mph | 23 mph |
| 60 km/h | 56.2 km/h | 37 mph | 35 mph |
| 80 km/h | 74.9 km/h | 50 mph | 47 mph |
| 100 km/h | 93.6 km/h | 62 mph | 58 mph |
| 120 km/h | 112.4 km/h | 75 mph | 70 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
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
-6.35%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 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 -6.35%. 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 | 37.5 km/h | 25 mph | 23 mph |
| 60 km/h | 56.2 km/h | 37 mph | 35 mph |
| 80 km/h | 74.9 km/h | 50 mph | 47 mph |
| 100 km/h | 93.6 km/h | 62 mph | 58 mph |
| 120 km/h | 112.4 km/h | 75 mph | 70 mph |
See individual specs: 275/65R20 · 275/55R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.