+5.06%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 285/70R17, fitting 315/70R17 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 42.0 km/h | 25 mph | 26 mph |
| 60 km/h | 63.0 km/h | 37 mph | 39 mph |
| 80 km/h | 84.0 km/h | 50 mph | 52 mph |
| 100 km/h | 105.1 km/h | 62 mph | 65 mph |
| 120 km/h | 126.1 km/h | 75 mph | 78 mph |
Full comparison
285/70R17
Overall diameter830.8 mm · 32.71 in
Section width285 mm · 11.22 in
Sidewall height199.5 mm · 7.85 in
Circumference2610.0 mm · 102.8 in
Revolutions per mile617
Revolutions per km383
315/70R17
Overall diameter872.8 mm · 34.36 in
Section width315 mm · 12.40 in
Sidewall height220.5 mm · 8.68 in
Circumference2742.0 mm · 108.0 in
Revolutions per mile587
Revolutions per km365
+5.06%Not recommended — recalibrate the speedometer
Original
Overall diameter830.8 mm · 32.71 in
Sidewall height199.5 mm
Circumference2,610 mm
Revolutions / mile616.6
New
Overall diameter872.8 mm · 34.36 in
Sidewall height220.5 mm
Circumference2,742 mm
Revolutions / mile586.9
Speedometer & odometer error
The new tire changes overall diameter by +5.06%. 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 | 42 km/h | 25 mph | 26 mph |
| 60 km/h | 63 km/h | 37 mph | 39 mph |
| 80 km/h | 84 km/h | 50 mph | 52 mph |
| 100 km/h | 105.1 km/h | 62 mph | 65 mph |
| 120 km/h | 126.1 km/h | 75 mph | 78 mph |
See individual specs: 285/70R17 · 315/70R17. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.