+0.35%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 215/60R17, fitting 235/50R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.1 km/h | 25 mph | 25 mph |
| 60 km/h | 60.2 km/h | 37 mph | 37 mph |
| 80 km/h | 80.3 km/h | 50 mph | 50 mph |
| 100 km/h | 100.3 km/h | 62 mph | 62 mph |
| 120 km/h | 120.4 km/h | 75 mph | 75 mph |
Full comparison
215/60R17
Overall diameter689.8 mm · 27.16 in
Section width215 mm · 8.46 in
Sidewall height129.0 mm · 5.08 in
Circumference2167.1 mm · 85.3 in
Revolutions per mile743
Revolutions per km461
235/50R18
Overall diameter692.2 mm · 27.25 in
Section width235 mm · 9.25 in
Sidewall height117.5 mm · 4.63 in
Circumference2174.6 mm · 85.6 in
Revolutions per mile740
Revolutions per km460
+0.35%Safe swap — speedometer error is minor
Original
Overall diameter689.8 mm · 27.16 in
Sidewall height129 mm
Circumference2,167.1 mm
Revolutions / mile742.6
New
Overall diameter692.2 mm · 27.25 in
Sidewall height117.5 mm
Circumference2,174.6 mm
Revolutions / mile740.1
Speedometer & odometer error
The new tire changes overall diameter by +0.35%. 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 | 40.1 km/h | 25 mph | 25 mph |
| 60 km/h | 60.2 km/h | 37 mph | 37 mph |
| 80 km/h | 80.3 km/h | 50 mph | 50 mph |
| 100 km/h | 100.3 km/h | 62 mph | 62 mph |
| 120 km/h | 120.4 km/h | 75 mph | 75 mph |
See individual specs: 215/60R17 · 235/50R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.