255/45R21 vs 285/45R21
285/45R21 is outside the ±3% rule as a replacement for 255/45R21: the diameter differs by +3.54%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 285/45R21 on a car calibrated for 255/45R21, the speedometer reads 57.9 mph when you're really doing 60, and the odometer under-counts by 3.5%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.1 mph |
| 45 mph | 46.6 mph |
| 60 mph | 62.1 mph |
| 70 mph | 72.5 mph |
| 80 mph | 82.8 mph |
Other sizes close to 255/45R21
- 255/45R21 vs 255/50R20+0.01%
- 255/45R21 vs 275/45R20-0.97%
- 255/45R21 vs 235/55R20+0.47%
- 255/45R21 vs 265/40R21-2.29%
- 255/45R21 vs 275/35R21-4.85%
- 255/45R21 vs 295/35R21-3.01%
- 255/45R21 vs 275/45R21+2.36%
- 255/45R21 vs 255/40R21-3.34%
- 255/45R21 vs 285/35R22-0.60%
- 255/45R21 vs 295/40R21+0.85%
- 255/45R21 vs 285/40R21-0.20%
- 255/45R21 vs 265/45R21+1.18%
Questions
Can I replace 255/45R21 with 285/45R21?
285/45R21 is outside the ±3% rule as a replacement for 255/45R21: the diameter differs by +3.54%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/45R21 and 285/45R21?
285/45R21 is 1.06" taller and 30 mm wider; the sidewall is +0.53". At an indicated 60 mph you'd actually be doing 62.1 mph.
Will 285/45R21 fit on 255/45R21 wheels?
Both use a 21" rim, so the wheel diameter matches; check the wheel's width range for a 285 mm tire and the fender clearance.