305/50R20 vs 305/55R20
305/55R20 is outside the ±3% rule as a replacement for 305/50R20: the diameter differs by +3.75%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 305/55R20 on a car calibrated for 305/50R20, the speedometer reads 57.8 mph when you're really doing 60, and the odometer under-counts by 3.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.1 mph |
| 45 mph | 46.7 mph |
| 60 mph | 62.3 mph |
| 70 mph | 72.6 mph |
| 80 mph | 83.0 mph |
Other sizes close to 305/50R20
- 305/50R20 vs 275/55R20-0.31%
- 305/50R20 vs 275/60R20+3.08%
- 305/50R20 vs 265/50R20-4.92%
- 305/50R20 vs 255/55R20-3.01%
- 305/50R20 vs 265/60R20+1.60%
- 305/50R20 vs 285/55R20+1.05%
- 305/50R20 vs 285/60R20+4.55%
- 305/50R20 vs 275/50R20-3.69%
- 305/50R20 vs 33x12.50R20+3.10%
- 305/50R20 vs 295/55R20+2.40%
- 305/50R20 vs 285/50R20-2.46%
- 305/50R20 vs 245/60R20-1.35%
Questions
Can I replace 305/50R20 with 305/55R20?
305/55R20 is outside the ±3% rule as a replacement for 305/50R20: the diameter differs by +3.75%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 305/50R20 and 305/55R20?
305/55R20 is 1.20" taller and 0 mm wider; the sidewall is +0.60". At an indicated 60 mph you'd actually be doing 62.3 mph.
Will 305/55R20 fit on 305/50R20 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.