285/45R21 vs 275/50R21
275/50R21 is a safe swap for 285/45R21 by the usual ±3% rule: the diameter differs by +2.34%.
Speedometer and odometer
With 275/50R21 on a car calibrated for 285/45R21, the speedometer reads 58.6 mph when you're really doing 60, and the odometer under-counts by 2.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.7 mph |
| 45 mph | 46.1 mph |
| 60 mph | 61.4 mph |
| 70 mph | 71.6 mph |
| 80 mph | 81.9 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 285/50R20+0.39%
- 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%
Questions
Can I replace 285/45R21 with 275/50R21?
275/50R21 is a safe swap for 285/45R21 by the usual ±3% rule: the diameter differs by +2.34%.
What's the difference between 285/45R21 and 275/50R21?
275/50R21 is 0.73" taller and 10 mm narrower; the sidewall is +0.36". At an indicated 60 mph you'd actually be doing 61.4 mph.
Will 275/50R21 fit on 285/45R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 275 mm tire and the fender clearance.