+1.43%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 275/60R20, fitting 285/60R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.6 km/h | 25 mph | 25 mph |
| 60 km/h | 60.9 km/h | 37 mph | 38 mph |
| 80 km/h | 81.1 km/h | 50 mph | 50 mph |
| 100 km/h | 101.4 km/h | 62 mph | 63 mph |
| 120 km/h | 121.7 km/h | 75 mph | 76 mph |
Full comparison
275/60R20
Overall diameter838.0 mm · 32.99 in
Section width275 mm · 10.83 in
Sidewall height165.0 mm · 6.50 in
Circumference2632.7 mm · 103.6 in
Revolutions per mile611
Revolutions per km380
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
+1.43%Safe swap — speedometer error is minor
Original
Overall diameter838 mm · 32.99 in
Sidewall height165 mm
Circumference2,632.7 mm
Revolutions / mile611.3
New
Overall diameter850 mm · 33.46 in
Sidewall height171 mm
Circumference2,670.4 mm
Revolutions / mile602.7
Speedometer & odometer error
The new tire changes overall diameter by +1.43%. 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 | 40.6 km/h | 25 mph | 25 mph |
| 60 km/h | 60.9 km/h | 37 mph | 38 mph |
| 80 km/h | 81.1 km/h | 50 mph | 50 mph |
| 100 km/h | 101.4 km/h | 62 mph | 63 mph |
| 120 km/h | 121.7 km/h | 75 mph | 76 mph |
See individual specs: 275/60R20 · 285/60R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.