-3.28%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 235/55R18, fitting 235/50R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.7 km/h | 25 mph | 24 mph |
| 60 km/h | 58.0 km/h | 37 mph | 36 mph |
| 80 km/h | 77.4 km/h | 50 mph | 48 mph |
| 100 km/h | 96.7 km/h | 62 mph | 60 mph |
| 120 km/h | 116.1 km/h | 75 mph | 72 mph |
Full comparison
235/55R18
Overall diameter715.7 mm · 28.18 in
Section width235 mm · 9.25 in
Sidewall height129.3 mm · 5.09 in
Circumference2248.4 mm · 88.5 in
Revolutions per mile716
Revolutions per km445
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
-3.28%Borderline — noticeable speedometer/odometer error
Original
Overall diameter715.7 mm · 28.18 in
Sidewall height129.3 mm
Circumference2,248.4 mm
Revolutions / mile715.8
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 -3.28%. 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 | 38.7 km/h | 25 mph | 24 mph |
| 60 km/h | 58 km/h | 37 mph | 36 mph |
| 80 km/h | 77.4 km/h | 50 mph | 48 mph |
| 100 km/h | 96.7 km/h | 62 mph | 60 mph |
| 120 km/h | 116.1 km/h | 75 mph | 72 mph |
See individual specs: 235/55R18 · 235/50R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.