-1.54%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 255/70R18, fitting 265/65R18 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.4 km/h | 25 mph | 24 mph |
| 60 km/h | 59.1 km/h | 37 mph | 37 mph |
| 80 km/h | 78.8 km/h | 50 mph | 49 mph |
| 100 km/h | 98.5 km/h | 62 mph | 61 mph |
| 120 km/h | 118.2 km/h | 75 mph | 73 mph |
Full comparison
255/70R18
Overall diameter814.2 mm · 32.06 in
Section width255 mm · 10.04 in
Sidewall height178.5 mm · 7.03 in
Circumference2557.9 mm · 100.7 in
Revolutions per mile629
Revolutions per km391
265/65R18
Overall diameter801.7 mm · 31.56 in
Section width265 mm · 10.43 in
Sidewall height172.3 mm · 6.78 in
Circumference2518.6 mm · 99.2 in
Revolutions per mile639
Revolutions per km397
-1.54%Safe swap — speedometer error is minor
Original
Overall diameter814.2 mm · 32.06 in
Sidewall height178.5 mm
Circumference2,557.9 mm
Revolutions / mile629.2
New
Overall diameter801.7 mm · 31.56 in
Sidewall height172.3 mm
Circumference2,518.6 mm
Revolutions / mile639
Speedometer & odometer error
The new tire changes overall diameter by -1.54%. 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 | 39.4 km/h | 25 mph | 24 mph |
| 60 km/h | 59.1 km/h | 37 mph | 37 mph |
| 80 km/h | 78.8 km/h | 50 mph | 49 mph |
| 100 km/h | 98.5 km/h | 62 mph | 61 mph |
| 120 km/h | 118.2 km/h | 75 mph | 73 mph |
See individual specs: 255/70R18 · 265/65R18. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.