-5.11%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 275/70R18, fitting 285/60R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.0 km/h | 25 mph | 24 mph |
| 60 km/h | 56.9 km/h | 37 mph | 35 mph |
| 80 km/h | 75.9 km/h | 50 mph | 47 mph |
| 100 km/h | 94.9 km/h | 62 mph | 59 mph |
| 120 km/h | 113.9 km/h | 75 mph | 71 mph |
Full comparison
275/70R18
Overall diameter842.2 mm · 33.16 in
Section width275 mm · 10.83 in
Sidewall height192.5 mm · 7.58 in
Circumference2645.8 mm · 104.2 in
Revolutions per mile608
Revolutions per km378
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
-5.11%Not recommended — recalibrate the speedometer
Original
Overall diameter842.2 mm · 33.16 in
Sidewall height192.5 mm
Circumference2,645.8 mm
Revolutions / mile608.3
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 -5.11%. 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 | 38 km/h | 25 mph | 24 mph |
| 60 km/h | 56.9 km/h | 37 mph | 35 mph |
| 80 km/h | 75.9 km/h | 50 mph | 47 mph |
| 100 km/h | 94.9 km/h | 62 mph | 59 mph |
| 120 km/h | 113.9 km/h | 75 mph | 71 mph |
See individual specs: 275/70R18 · 285/60R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.