-2.06%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 275/45R20, fitting 295/35R21 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 39.2 km/h | 25 mph | 24 mph |
| 60 km/h | 58.8 km/h | 37 mph | 37 mph |
| 80 km/h | 78.3 km/h | 50 mph | 49 mph |
| 100 km/h | 97.9 km/h | 62 mph | 61 mph |
| 120 km/h | 117.5 km/h | 75 mph | 73 mph |
Full comparison
275/45R20
Overall diameter755.5 mm · 29.74 in
Section width275 mm · 10.83 in
Sidewall height123.8 mm · 4.87 in
Circumference2373.5 mm · 93.4 in
Revolutions per mile678
Revolutions per km421
295/35R21
Overall diameter739.9 mm · 29.13 in
Section width295 mm · 11.61 in
Sidewall height103.3 mm · 4.06 in
Circumference2324.5 mm · 91.5 in
Revolutions per mile692
Revolutions per km430
-2.06%Safe swap — speedometer error is minor
Original
Overall diameter755.5 mm · 29.74 in
Sidewall height123.8 mm
Circumference2,373.5 mm
Revolutions / mile678.1
New
Overall diameter739.9 mm · 29.13 in
Sidewall height103.3 mm
Circumference2,324.5 mm
Revolutions / mile692.4
Speedometer & odometer error
The new tire changes overall diameter by -2.06%. 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 | 39.2 km/h | 25 mph | 24 mph |
| 60 km/h | 58.8 km/h | 37 mph | 37 mph |
| 80 km/h | 78.3 km/h | 50 mph | 49 mph |
| 100 km/h | 97.9 km/h | 62 mph | 61 mph |
| 120 km/h | 117.5 km/h | 75 mph | 73 mph |
See individual specs: 275/45R20 · 295/35R21. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.