+3.15%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 245/70R17, fitting 285/60R18 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 | 61.9 km/h | 37 mph | 38 mph |
| 80 km/h | 82.5 km/h | 50 mph | 51 mph |
| 100 km/h | 103.1 km/h | 62 mph | 64 mph |
| 120 km/h | 123.8 km/h | 75 mph | 77 mph |
Full comparison
245/70R17
Overall diameter774.8 mm · 30.50 in
Section width245 mm · 9.65 in
Sidewall height171.5 mm · 6.75 in
Circumference2434.1 mm · 95.8 in
Revolutions per mile661
Revolutions per km411
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
+3.15%Borderline — noticeable speedometer/odometer error
Original
Overall diameter774.8 mm · 30.5 in
Sidewall height171.5 mm
Circumference2,434.1 mm
Revolutions / mile661.2
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 +3.15%. 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 | 41.3 km/h | 25 mph | 26 mph |
| 60 km/h | 61.9 km/h | 37 mph | 38 mph |
| 80 km/h | 82.5 km/h | 50 mph | 51 mph |
| 100 km/h | 103.1 km/h | 62 mph | 64 mph |
| 120 km/h | 123.8 km/h | 75 mph | 77 mph |
See individual specs: 245/70R17 · 285/60R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.