305/50R20 vs 255/60R20
255/60R20 is a safe swap for 305/50R20 by the usual ±3% rule: the diameter differs by +0.12%.
Speedometer and odometer
With 255/60R20 on a car calibrated for 305/50R20, the speedometer reads 59.9 mph when you're really doing 60, and the odometer under-counts by 0.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.0 mph |
| 45 mph | 45.1 mph |
| 60 mph | 60.1 mph |
| 70 mph | 70.1 mph |
| 80 mph | 80.1 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 305/55R20+3.75%
- 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%
Questions
Can I replace 305/50R20 with 255/60R20?
255/60R20 is a safe swap for 305/50R20 by the usual ±3% rule: the diameter differs by +0.12%.
What's the difference between 305/50R20 and 255/60R20?
255/60R20 is 0.04" taller and 50 mm narrower; the sidewall is +0.02". At an indicated 60 mph you'd actually be doing 60.1 mph.
Will 255/60R20 fit on 305/50R20 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.