285/45R21 vs 285/50R20
285/50R20 is a safe swap for 285/45R21 by the usual ±3% rule: the diameter differs by +0.39%.
Speedometer and odometer
With 285/50R20 on a car calibrated for 285/45R21, the speedometer reads 59.8 mph when you're really doing 60, and the odometer under-counts by 0.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.2 mph |
| 60 mph | 60.2 mph |
| 70 mph | 70.3 mph |
| 80 mph | 80.3 mph |
Other sizes close to 285/45R21
- 285/45R21 vs 255/55R20-0.18%
- 285/45R21 vs 275/50R20-0.87%
- 285/45R21 vs 275/45R21-1.14%
- 285/45R21 vs 285/40R22-0.39%
- 285/45R21 vs 295/40R21-2.60%
- 285/45R21 vs 265/45R21-2.28%
- 285/45R21 vs 285/40R21-3.61%
- 285/45R21 vs 275/40R21-4.62%
- 285/45R21 vs 315/35R21-4.56%
- 285/45R21 vs 315/40R21-0.57%
- 285/45R21 vs 325/35R22-0.46%
- 285/45R21 vs 255/45R21-3.42%
Questions
Can I replace 285/45R21 with 285/50R20?
285/50R20 is a safe swap for 285/45R21 by the usual ±3% rule: the diameter differs by +0.39%.
What's the difference between 285/45R21 and 285/50R20?
285/50R20 is 0.12" taller and 0 mm wider; the sidewall is +0.56". At an indicated 60 mph you'd actually be doing 60.2 mph.
Will 285/50R20 fit on 285/45R21 wheels?
No — 285/45R21 needs a 21" wheel and 285/50R20 a 20" wheel. This is a plus/minus-size swap that changes wheels too.