+3.35%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 285/60R20, fitting 285/65R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 41.3 km/h | 25 mph | 26 mph |
| 60 km/h | 62.0 km/h | 37 mph | 39 mph |
| 80 km/h | 82.7 km/h | 50 mph | 51 mph |
| 100 km/h | 103.4 km/h | 62 mph | 64 mph |
| 120 km/h | 124.0 km/h | 75 mph | 77 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
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
+3.35%Borderline — noticeable speedometer/odometer error
Original
Overall diameter850 mm · 33.46 in
Sidewall height171 mm
Circumference2,670.4 mm
Revolutions / mile602.7
New
Overall diameter878.5 mm · 34.59 in
Sidewall height185.3 mm
Circumference2,759.9 mm
Revolutions / mile583.1
Speedometer & odometer error
The new tire changes overall diameter by +3.35%. 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 | 41.3 km/h | 25 mph | 26 mph |
| 60 km/h | 62 km/h | 37 mph | 39 mph |
| 80 km/h | 82.7 km/h | 50 mph | 51 mph |
| 100 km/h | 103.4 km/h | 62 mph | 64 mph |
| 120 km/h | 124 km/h | 75 mph | 77 mph |
See individual specs: 285/60R20 · 285/65R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.