+7.51%Not recommended — recalibrate the speedometer
Speedometer error
With a speedometer calibrated to 275/65R20, fitting 325/65R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 43.0 km/h | 25 mph | 27 mph |
| 60 km/h | 64.5 km/h | 37 mph | 40 mph |
| 80 km/h | 86.0 km/h | 50 mph | 53 mph |
| 100 km/h | 107.5 km/h | 62 mph | 67 mph |
| 120 km/h | 129.0 km/h | 75 mph | 80 mph |
Full comparison
275/65R20
Overall diameter865.5 mm · 34.07 in
Section width275 mm · 10.83 in
Sidewall height178.8 mm · 7.04 in
Circumference2719.0 mm · 107.0 in
Revolutions per mile592
Revolutions per km368
325/65R20
Overall diameter930.5 mm · 36.63 in
Section width325 mm · 12.80 in
Sidewall height211.3 mm · 8.32 in
Circumference2923.3 mm · 115.1 in
Revolutions per mile551
Revolutions per km342
+7.51%Not recommended — recalibrate the speedometer
Original
Overall diameter865.5 mm · 34.07 in
Sidewall height178.8 mm
Circumference2,719 mm
Revolutions / mile591.9
New
Overall diameter930.5 mm · 36.63 in
Sidewall height211.3 mm
Circumference2,923.3 mm
Revolutions / mile550.5
Speedometer & odometer error
The new tire changes overall diameter by +7.51%. 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 | 43 km/h | 25 mph | 27 mph |
| 60 km/h | 64.5 km/h | 37 mph | 40 mph |
| 80 km/h | 86 km/h | 50 mph | 53 mph |
| 100 km/h | 107.5 km/h | 62 mph | 67 mph |
| 120 km/h | 129 km/h | 75 mph | 80 mph |
See individual specs: 275/65R20 · 325/65R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.