285/45R20 vs 255/55R20
255/55R20 is outside the ±3% rule as a replacement for 285/45R20: the diameter differs by +3.14%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/55R20 on a car calibrated for 285/45R20, the speedometer reads 58.2 mph when you're really doing 60, and the odometer under-counts by 3.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.9 mph |
| 45 mph | 46.4 mph |
| 60 mph | 61.9 mph |
| 70 mph | 72.2 mph |
| 80 mph | 82.5 mph |
Other sizes close to 285/45R20
- 285/45R20 vs 245/45R20-4.71%
- 285/45R20 vs 255/45R20-3.53%
- 285/45R20 vs 255/50R20-0.20%
- 285/45R20 vs 275/40R20-4.77%
- 285/45R20 vs 265/50R20+1.11%
- 285/45R20 vs 245/50R20-1.50%
- 285/45R20 vs 275/45R20-1.18%
- 285/45R20 vs 235/55R20+0.26%
- 285/45R20 vs 265/45R20-2.35%
- 285/45R20 vs 255/55R19-0.18%
- 285/45R20 vs 315/35R20-4.71%
- 285/45R20 vs 275/50R20+2.42%
Questions
Can I replace 285/45R20 with 255/55R20?
255/55R20 is outside the ±3% rule as a replacement for 285/45R20: the diameter differs by +3.14%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 285/45R20 and 255/55R20?
255/55R20 is 0.94" taller and 30 mm narrower; the sidewall is +0.47". At an indicated 60 mph you'd actually be doing 61.9 mph.
Will 255/55R20 fit on 285/45R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.