-2.69%Safe swap — speedometer error is minor
Speedometer error
With a speedometer calibrated to 295/35R21, fitting 265/40R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 38.9 km/h | 25 mph | 24 mph |
| 60 km/h | 58.4 km/h | 37 mph | 36 mph |
| 80 km/h | 77.8 km/h | 50 mph | 48 mph |
| 100 km/h | 97.3 km/h | 62 mph | 60 mph |
| 120 km/h | 116.8 km/h | 75 mph | 73 mph |
Full comparison
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
265/40R20
Overall diameter720.0 mm · 28.35 in
Section width265 mm · 10.43 in
Sidewall height106.0 mm · 4.17 in
Circumference2261.9 mm · 89.1 in
Revolutions per mile711
Revolutions per km442
-2.69%Safe swap — speedometer error is minor
Original
Overall diameter739.9 mm · 29.13 in
Sidewall height103.3 mm
Circumference2,324.5 mm
Revolutions / mile692.4
New
Overall diameter720 mm · 28.35 in
Sidewall height106 mm
Circumference2,261.9 mm
Revolutions / mile711.5
Speedometer & odometer error
The new tire changes overall diameter by -2.69%. 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 | 38.9 km/h | 25 mph | 24 mph |
| 60 km/h | 58.4 km/h | 37 mph | 36 mph |
| 80 km/h | 77.8 km/h | 50 mph | 48 mph |
| 100 km/h | 97.3 km/h | 62 mph | 60 mph |
| 120 km/h | 116.8 km/h | 75 mph | 73 mph |
See individual specs: 295/35R21 · 265/40R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.