-3.05%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 245/70R17, fitting 245/60R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.8 km/h | 25 mph | 24 mph |
| 60 km/h | 58.2 km/h | 37 mph | 36 mph |
| 80 km/h | 77.6 km/h | 50 mph | 48 mph |
| 100 km/h | 97.0 km/h | 62 mph | 60 mph |
| 120 km/h | 116.3 km/h | 75 mph | 72 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
245/60R18
Overall diameter751.2 mm · 29.57 in
Section width245 mm · 9.65 in
Sidewall height147.0 mm · 5.79 in
Circumference2360.0 mm · 92.9 in
Revolutions per mile682
Revolutions per km424
-3.05%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 diameter751.2 mm · 29.57 in
Sidewall height147 mm
Circumference2,360 mm
Revolutions / mile681.9
Speedometer & odometer error
The new tire changes overall diameter by -3.05%. 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 | 38.8 km/h | 25 mph | 24 mph |
| 60 km/h | 58.2 km/h | 37 mph | 36 mph |
| 80 km/h | 77.6 km/h | 50 mph | 48 mph |
| 100 km/h | 97 km/h | 62 mph | 60 mph |
| 120 km/h | 116.3 km/h | 75 mph | 72 mph |
See individual specs: 245/70R17 · 245/60R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.