255/55R20 vs 305/50R20
305/50R20 is outside the ±3% rule as a replacement for 255/55R20: the diameter differs by +3.11%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 305/50R20 on a car calibrated for 255/55R20, 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 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 285/55R20+4.19%
- 255/55R20 vs 275/50R20-0.70%
- 255/55R20 vs 275/45R21-0.96%
- 255/55R20 vs 285/50R20+0.57%
Questions
Can I replace 255/55R20 with 305/50R20?
305/50R20 is outside the ±3% rule as a replacement for 255/55R20: the diameter differs by +3.11%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/55R20 and 305/50R20?
305/50R20 is 0.96" taller and 50 mm wider; the sidewall is +0.48". At an indicated 60 mph you'd actually be doing 61.9 mph.
Will 305/50R20 fit on 255/55R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 305 mm tire and the fender clearance.