The new tire changes overall diameter by -15.34%. 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 | 33.9 km/h | 25 mph | 21 mph |
| 60 km/h | 50.8 km/h | 37 mph | 32 mph |
| 80 km/h | 67.7 km/h | 50 mph | 42 mph |
| 100 km/h | 84.7 km/h | 62 mph | 53 mph |
| 120 km/h | 101.6 km/h | 75 mph | 63 mph |
Commonly compared with 285/45R21
- 285/45R21 vs 285/50R20 · 285/50R20 specs
- 285/45R21 vs 275/45R21 · 275/45R21 specs
- 285/45R21 vs 305/40R22 · 305/40R22 specs
- 285/45R21 vs 265/50R20 · 265/50R20 specs
- 285/45R21 vs 265/45R21 · 265/45R21 specs
- 285/45R21 vs 265/40R22 · 265/40R22 specs
- 285/45R21 vs 275/55R20 · 275/55R20 specs
- 285/45R21 vs 285/45R22 · 285/45R22 specs
FAQ
What is the overall diameter of a 285/45R21 tire?
A 285/45R21 tire has an overall diameter of about 31.10 inches (790 mm) and a section width of 285 mm.
What sizes can replace a 285/45R21 tire?
Sizes within about ±3% of 285/45R21's 31.1-inch diameter are the closest matches, such as 285/50R20, 275/45R21, 305/40R22. 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.