+0.59%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 285/35R22, fitting 255/40R22 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 40.2 km/h | 25 mph | 25 mph |
| 60 km/h | 60.4 km/h | 37 mph | 38 mph |
| 80 km/h | 80.5 km/h | 50 mph | 50 mph |
| 100 km/h | 100.6 km/h | 62 mph | 63 mph |
| 120 km/h | 120.7 km/h | 75 mph | 75 mph |
Full comparison
285/35R22
Overall diameter758.3 mm · 29.85 in
Section width285 mm · 11.22 in
Sidewall height99.8 mm · 3.93 in
Circumference2382.3 mm · 93.8 in
Revolutions per mile676
Revolutions per km420
255/40R22
Overall diameter762.8 mm · 30.03 in
Section width255 mm · 10.04 in
Sidewall height102.0 mm · 4.02 in
Circumference2396.4 mm · 94.3 in
Revolutions per mile672
Revolutions per km417
+0.59%Safe swap — speedometer error is minor
Original
Overall diameter758.3 mm · 29.85 in
Sidewall height99.8 mm
Circumference2,382.3 mm
Revolutions / mile675.6
New
Overall diameter762.8 mm · 30.03 in
Sidewall height102 mm
Circumference2,396.4 mm
Revolutions / mile671.6
Speedometer & odometer error
The new tire changes overall diameter by +0.59%. 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 | 40.2 km/h | 25 mph | 25 mph |
| 60 km/h | 60.4 km/h | 37 mph | 38 mph |
| 80 km/h | 80.5 km/h | 50 mph | 50 mph |
| 100 km/h | 100.6 km/h | 62 mph | 63 mph |
| 120 km/h | 120.7 km/h | 75 mph | 75 mph |
See individual specs: 285/35R22 · 255/40R22. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.