+2.06%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 225/65R17, fitting 235/60R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.8 km/h | 25 mph | 25 mph |
| 60 km/h | 61.2 km/h | 37 mph | 38 mph |
| 80 km/h | 81.6 km/h | 50 mph | 51 mph |
| 100 km/h | 102.1 km/h | 62 mph | 63 mph |
| 120 km/h | 122.5 km/h | 75 mph | 76 mph |
Full comparison
225/65R17
Overall diameter724.3 mm · 28.52 in
Section width225 mm · 8.86 in
Sidewall height146.3 mm · 5.76 in
Circumference2275.5 mm · 89.6 in
Revolutions per mile707
Revolutions per km439
235/60R18
Overall diameter739.2 mm · 29.10 in
Section width235 mm · 9.25 in
Sidewall height141.0 mm · 5.55 in
Circumference2322.3 mm · 91.4 in
Revolutions per mile693
Revolutions per km431
+2.06%Safe swap — speedometer error is minor
Original
Overall diameter724.3 mm · 28.52 in
Sidewall height146.3 mm
Circumference2,275.5 mm
Revolutions / mile707.3
New
Overall diameter739.2 mm · 29.1 in
Sidewall height141 mm
Circumference2,322.3 mm
Revolutions / mile693
Speedometer & odometer error
The new tire changes overall diameter by +2.06%. 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 | 40.8 km/h | 25 mph | 25 mph |
| 60 km/h | 61.2 km/h | 37 mph | 38 mph |
| 80 km/h | 81.6 km/h | 50 mph | 51 mph |
| 100 km/h | 102.1 km/h | 62 mph | 63 mph |
| 120 km/h | 122.5 km/h | 75 mph | 76 mph |
See individual specs: 225/65R17 · 235/60R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.