235/55R20 vs 285/50R20
285/50R20 is outside the ±3% rule as a replacement for 235/55R20: the diameter differs by +3.46%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 285/50R20 on a car calibrated for 235/55R20, the speedometer reads 58.0 mph when you're really doing 60, and the odometer under-counts by 3.5%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.0 mph |
| 45 mph | 46.6 mph |
| 60 mph | 62.1 mph |
| 70 mph | 72.4 mph |
| 80 mph | 82.8 mph |
Other sizes close to 235/55R20
- 235/55R20 vs 245/45R20-4.96%
- 235/55R20 vs 255/45R20-3.78%
- 235/55R20 vs 255/50R20-0.46%
- 235/55R20 vs 265/50R20+0.85%
- 235/55R20 vs 245/50R20-1.76%
- 235/55R20 vs 275/45R20-1.44%
- 235/55R20 vs 255/55R20+2.87%
- 235/55R20 vs 265/45R20-2.61%
- 235/55R20 vs 255/55R19-0.44%
- 235/55R20 vs 315/35R20-4.96%
- 235/55R20 vs 275/50R20+2.15%
- 235/55R20 vs 295/40R20-2.94%
Questions
Can I replace 235/55R20 with 285/50R20?
285/50R20 is outside the ±3% rule as a replacement for 235/55R20: the diameter differs by +3.46%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 235/55R20 and 285/50R20?
285/50R20 is 1.04" taller and 50 mm wider; the sidewall is +0.52". At an indicated 60 mph you'd actually be doing 62.1 mph.
Will 285/50R20 fit on 235/55R20 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.