-7.84%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 305/40R22, fitting 295/35R21 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 36.9 km/h | 25 mph | 23 mph |
| 60 km/h | 55.3 km/h | 37 mph | 34 mph |
| 80 km/h | 73.7 km/h | 50 mph | 46 mph |
| 100 km/h | 92.2 km/h | 62 mph | 57 mph |
| 120 km/h | 110.6 km/h | 75 mph | 69 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
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
-7.84%Not recommended — recalibrate the speedometer
Original
Overall diameter802.8 mm · 31.61 in
Sidewall height122 mm
Circumference2,522.1 mm
Revolutions / mile638.1
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 -7.84%. 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 | 36.9 km/h | 25 mph | 23 mph |
| 60 km/h | 55.3 km/h | 37 mph | 34 mph |
| 80 km/h | 73.7 km/h | 50 mph | 46 mph |
| 100 km/h | 92.2 km/h | 62 mph | 57 mph |
| 120 km/h | 110.6 km/h | 75 mph | 69 mph |
See individual specs: 305/40R22 · 295/35R21. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.