-3.51%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 315/70R17, fitting 275/70R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.6 km/h | 25 mph | 24 mph |
| 60 km/h | 57.9 km/h | 37 mph | 36 mph |
| 80 km/h | 77.2 km/h | 50 mph | 48 mph |
| 100 km/h | 96.5 km/h | 62 mph | 60 mph |
| 120 km/h | 115.8 km/h | 75 mph | 72 mph |
Full comparison
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
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
-3.51%Borderline — noticeable speedometer/odometer error
Original
Overall diameter872.8 mm · 34.36 in
Sidewall height220.5 mm
Circumference2,742 mm
Revolutions / mile586.9
New
Overall diameter842.2 mm · 33.16 in
Sidewall height192.5 mm
Circumference2,645.8 mm
Revolutions / mile608.3
Speedometer & odometer error
The new tire changes overall diameter by -3.51%. 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 | 38.6 km/h | 25 mph | 24 mph |
| 60 km/h | 57.9 km/h | 37 mph | 36 mph |
| 80 km/h | 77.2 km/h | 50 mph | 48 mph |
| 100 km/h | 96.5 km/h | 62 mph | 60 mph |
| 120 km/h | 115.8 km/h | 75 mph | 72 mph |
See individual specs: 315/70R17 · 275/70R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.