+2.80%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 275/45R21, fitting 305/40R22 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 41.1 km/h | 25 mph | 26 mph |
| 60 km/h | 61.7 km/h | 37 mph | 38 mph |
| 80 km/h | 82.2 km/h | 50 mph | 51 mph |
| 100 km/h | 102.8 km/h | 62 mph | 64 mph |
| 120 km/h | 123.4 km/h | 75 mph | 77 mph |
Full comparison
275/45R21
Overall diameter780.9 mm · 30.74 in
Section width275 mm · 10.83 in
Sidewall height123.8 mm · 4.87 in
Circumference2453.3 mm · 96.6 in
Revolutions per mile656
Revolutions per km408
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
+2.8%Safe swap — speedometer error is minor
Original
Overall diameter780.9 mm · 30.74 in
Sidewall height123.8 mm
Circumference2,453.3 mm
Revolutions / mile656
New
Overall diameter802.8 mm · 31.61 in
Sidewall height122 mm
Circumference2,522.1 mm
Revolutions / mile638.1
Speedometer & odometer error
The new tire changes overall diameter by +2.8%. 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 | 41.1 km/h | 25 mph | 26 mph |
| 60 km/h | 61.7 km/h | 37 mph | 38 mph |
| 80 km/h | 82.2 km/h | 50 mph | 51 mph |
| 100 km/h | 102.8 km/h | 62 mph | 64 mph |
| 120 km/h | 123.4 km/h | 75 mph | 77 mph |
See individual specs: 275/45R21 · 305/40R22. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.