-2.15%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 275/70R17, fitting 285/60R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.1 km/h | 25 mph | 24 mph |
| 60 km/h | 58.7 km/h | 37 mph | 36 mph |
| 80 km/h | 78.3 km/h | 50 mph | 49 mph |
| 100 km/h | 97.8 km/h | 62 mph | 61 mph |
| 120 km/h | 117.4 km/h | 75 mph | 73 mph |
Full comparison
275/70R17
Overall diameter816.8 mm · 32.16 in
Section width275 mm · 10.83 in
Sidewall height192.5 mm · 7.58 in
Circumference2566.1 mm · 101.0 in
Revolutions per mile627
Revolutions per km390
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
-2.15%Safe swap — speedometer error is minor
Original
Overall diameter816.8 mm · 32.16 in
Sidewall height192.5 mm
Circumference2,566.1 mm
Revolutions / mile627.2
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 -2.15%. 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 | 39.1 km/h | 25 mph | 24 mph |
| 60 km/h | 58.7 km/h | 37 mph | 36 mph |
| 80 km/h | 78.3 km/h | 50 mph | 49 mph |
| 100 km/h | 97.8 km/h | 62 mph | 61 mph |
| 120 km/h | 117.4 km/h | 75 mph | 73 mph |
See individual specs: 275/70R17 · 285/60R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.