-1.69%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 265/65R17, fitting 255/60R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.3 km/h | 25 mph | 24 mph |
| 60 km/h | 59.0 km/h | 37 mph | 37 mph |
| 80 km/h | 78.7 km/h | 50 mph | 49 mph |
| 100 km/h | 98.3 km/h | 62 mph | 61 mph |
| 120 km/h | 118.0 km/h | 75 mph | 73 mph |
Full comparison
265/65R17
Overall diameter776.3 mm · 30.56 in
Section width265 mm · 10.43 in
Sidewall height172.3 mm · 6.78 in
Circumference2438.8 mm · 96.0 in
Revolutions per mile660
Revolutions per km410
255/60R18
Overall diameter763.2 mm · 30.05 in
Section width255 mm · 10.04 in
Sidewall height153.0 mm · 6.02 in
Circumference2397.7 mm · 94.4 in
Revolutions per mile671
Revolutions per km417
-1.69%Safe swap — speedometer error is minor
Original
Overall diameter776.3 mm · 30.56 in
Sidewall height172.3 mm
Circumference2,438.8 mm
Revolutions / mile659.9
New
Overall diameter763.2 mm · 30.05 in
Sidewall height153 mm
Circumference2,397.7 mm
Revolutions / mile671.2
Speedometer & odometer error
The new tire changes overall diameter by -1.69%. 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 | 39.3 km/h | 25 mph | 24 mph |
| 60 km/h | 59 km/h | 37 mph | 37 mph |
| 80 km/h | 78.7 km/h | 50 mph | 49 mph |
| 100 km/h | 98.3 km/h | 62 mph | 61 mph |
| 120 km/h | 118 km/h | 75 mph | 73 mph |
See individual specs: 265/65R17 · 255/60R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.