255/55R20 vs 285/55R20
285/55R20 is outside the ±3% rule as a replacement for 255/55R20: the diameter differs by +4.19%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 285/55R20 on a car calibrated for 255/55R20, the speedometer reads 57.6 mph when you're really doing 60, and the odometer under-counts by 4.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.3 mph |
| 45 mph | 46.9 mph |
| 60 mph | 62.5 mph |
| 70 mph | 72.9 mph |
| 80 mph | 83.3 mph |
Other sizes close to 255/55R20
- 255/55R20 vs 275/55R20+2.79%
- 255/55R20 vs 255/50R20-3.23%
- 255/55R20 vs 265/50R20-1.97%
- 255/55R20 vs 245/50R20-4.50%
- 255/55R20 vs 275/45R20-4.19%
- 255/55R20 vs 235/55R20-2.79%
- 255/55R20 vs 255/60R19+0.01%
- 255/55R20 vs 265/60R20+4.76%
- 255/55R20 vs 275/50R20-0.70%
- 255/55R20 vs 275/45R21-0.96%
- 255/55R20 vs 285/50R20+0.57%
- 255/55R20 vs 285/45R21+0.18%
Questions
Can I replace 255/55R20 with 285/55R20?
285/55R20 is outside the ±3% rule as a replacement for 255/55R20: the diameter differs by +4.19%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/55R20 and 285/55R20?
285/55R20 is 1.30" taller and 30 mm wider; the sidewall is +0.65". At an indicated 60 mph you'd actually be doing 62.5 mph.
Will 285/55R20 fit on 255/55R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 285 mm tire and the fender clearance.