-4.98%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 305/40R22, fitting 255/40R22 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.0 km/h | 25 mph | 24 mph |
| 60 km/h | 57.0 km/h | 37 mph | 35 mph |
| 80 km/h | 76.0 km/h | 50 mph | 47 mph |
| 100 km/h | 95.0 km/h | 62 mph | 59 mph |
| 120 km/h | 114.0 km/h | 75 mph | 71 mph |
Full comparison
305/40R22
Overall diameter802.8 mm · 31.61 in
Section width305 mm · 12.01 in
Sidewall height122.0 mm · 4.80 in
Circumference2522.1 mm · 99.3 in
Revolutions per mile638
Revolutions per km396
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
-4.98%Borderline — noticeable speedometer/odometer error
Original
Overall diameter802.8 mm · 31.61 in
Sidewall height122 mm
Circumference2,522.1 mm
Revolutions / mile638.1
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 -4.98%. 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 | 38 km/h | 25 mph | 24 mph |
| 60 km/h | 57 km/h | 37 mph | 35 mph |
| 80 km/h | 76 km/h | 50 mph | 47 mph |
| 100 km/h | 95 km/h | 62 mph | 59 mph |
| 120 km/h | 114 km/h | 75 mph | 71 mph |
See individual specs: 305/40R22 · 255/40R22. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.