-0.45%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 265/70R17, fitting 285/60R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.8 km/h | 25 mph | 25 mph |
| 60 km/h | 59.7 km/h | 37 mph | 37 mph |
| 80 km/h | 79.6 km/h | 50 mph | 49 mph |
| 100 km/h | 99.6 km/h | 62 mph | 62 mph |
| 120 km/h | 119.5 km/h | 75 mph | 74 mph |
Full comparison
265/70R17
Overall diameter802.8 mm · 31.61 in
Section width265 mm · 10.43 in
Sidewall height185.5 mm · 7.30 in
Circumference2522.1 mm · 99.3 in
Revolutions per mile638
Revolutions per km396
285/60R18
Overall diameter799.2 mm · 31.46 in
Section width285 mm · 11.22 in
Sidewall height171.0 mm · 6.73 in
Circumference2510.8 mm · 98.8 in
Revolutions per mile641
Revolutions per km398
-0.45%Safe swap — speedometer error is minor
Original
Overall diameter802.8 mm · 31.61 in
Sidewall height185.5 mm
Circumference2,522.1 mm
Revolutions / mile638.1
New
Overall diameter799.2 mm · 31.46 in
Sidewall height171 mm
Circumference2,510.8 mm
Revolutions / mile641
Speedometer & odometer error
The new tire changes overall diameter by -0.45%. 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 | 39.8 km/h | 25 mph | 25 mph |
| 60 km/h | 59.7 km/h | 37 mph | 37 mph |
| 80 km/h | 79.6 km/h | 50 mph | 49 mph |
| 100 km/h | 99.6 km/h | 62 mph | 62 mph |
| 120 km/h | 119.5 km/h | 75 mph | 74 mph |
See individual specs: 265/70R17 · 285/60R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.