The new tire changes overall diameter by -20.72%. 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 | 31.7 km/h | 25 mph | 20 mph |
| 60 km/h | 47.6 km/h | 37 mph | 30 mph |
| 80 km/h | 63.4 km/h | 50 mph | 39 mph |
| 100 km/h | 79.3 km/h | 62 mph | 49 mph |
| 120 km/h | 95.1 km/h | 75 mph | 59 mph |
Commonly compared with 305/55R20
- 305/55R20 vs 275/60R20 · 275/60R20 specs
- 305/55R20 vs 285/60R20 · 285/60R20 specs
- 305/55R20 vs 285/55R20 · 285/55R20 specs
- 305/55R20 vs 275/65R20 · 275/65R20 specs
- 305/55R20 vs 275/55R20 · 275/55R20 specs
- 305/55R20 vs 285/65R20 · 285/65R20 specs
- 305/55R20 vs 285/50R20 · 285/50R20 specs
- 305/55R20 vs 285/45R21 · 285/45R21 specs
FAQ
What is the overall diameter of a 305/55R20 tire?
A 305/55R20 tire has an overall diameter of about 33.21 inches (844 mm) and a section width of 305 mm.
What sizes can replace a 305/55R20 tire?
Sizes within about ±3% of 305/55R20's 33.2-inch diameter are the closest matches, such as 275/60R20, 285/60R20, 285/55R20. Use the calculator above to check the exact speedometer effect of any substitute.
Fitment & trouble codes
Changing tire size by more than about 3% shifts the speedometer, odometer and, on some vehicles, ABS/traction calibration — which can set wheel-speed-sensor or vehicle-speed codes. See C1234 (wheel speed sensor) and C0050 (rear wheel speed) if a warning light appears after a size change.