+3.48%Borderline — noticeable speedometer/odometer error
Speedometer error
With a speedometer calibrated to 245/40R20, fitting 245/45R20 makes it read as follows:
| Speedo shows | True speed | Speedo shows | True speed |
|---|---|---|---|
| 40 km/h | 41.4 km/h | 25 mph | 26 mph |
| 60 km/h | 62.1 km/h | 37 mph | 39 mph |
| 80 km/h | 82.8 km/h | 50 mph | 51 mph |
| 100 km/h | 103.5 km/h | 62 mph | 64 mph |
| 120 km/h | 124.2 km/h | 75 mph | 77 mph |
Full comparison
245/40R20
Overall diameter704.0 mm · 27.72 in
Section width245 mm · 9.65 in
Sidewall height98.0 mm · 3.86 in
Circumference2211.7 mm · 87.1 in
Revolutions per mile728
Revolutions per km452
245/45R20
Overall diameter728.5 mm · 28.68 in
Section width245 mm · 9.65 in
Sidewall height110.3 mm · 4.34 in
Circumference2288.7 mm · 90.1 in
Revolutions per mile703
Revolutions per km437
+3.48%Borderline — noticeable speedometer/odometer error
Original
Overall diameter704 mm · 27.72 in
Sidewall height98 mm
Circumference2,211.7 mm
Revolutions / mile727.7
New
Overall diameter728.5 mm · 28.68 in
Sidewall height110.3 mm
Circumference2,288.7 mm
Revolutions / mile703.2
Speedometer & odometer error
The new tire changes overall diameter by +3.48%. 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 | 41.4 km/h | 25 mph | 26 mph |
| 60 km/h | 62.1 km/h | 37 mph | 39 mph |
| 80 km/h | 82.8 km/h | 50 mph | 51 mph |
| 100 km/h | 103.5 km/h | 62 mph | 64 mph |
| 120 km/h | 124.2 km/h | 75 mph | 77 mph |
See individual specs: 245/40R20 · 245/45R20. A change this size can affect ABS/speed calibration — see wheel-speed codes if a light appears.