+3.02%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 235/55R18, fitting 235/65R17 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 41.2 km/h | 25 mph | 26 mph |
| 60 km/h | 61.8 km/h | 37 mph | 38 mph |
| 80 km/h | 82.4 km/h | 50 mph | 51 mph |
| 100 km/h | 103.0 km/h | 62 mph | 64 mph |
| 120 km/h | 123.6 km/h | 75 mph | 77 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
235/65R17
Overall diameter737.3 mm · 29.03 in
Section width235 mm · 9.25 in
Sidewall height152.8 mm · 6.01 in
Circumference2316.3 mm · 91.2 in
Revolutions per mile695
Revolutions per km432
+3.02%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 diameter737.3 mm · 29.03 in
Sidewall height152.8 mm
Circumference2,316.3 mm
Revolutions / mile694.8
Speedometer & odometer error
The new tire changes overall diameter by +3.02%. 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 | 41.2 km/h | 25 mph | 26 mph |
| 60 km/h | 61.8 km/h | 37 mph | 38 mph |
| 80 km/h | 82.4 km/h | 50 mph | 51 mph |
| 100 km/h | 103 km/h | 62 mph | 64 mph |
| 120 km/h | 123.6 km/h | 75 mph | 77 mph |
See individual specs: 235/55R18 · 235/65R17. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.