285/50R20 vs 305/50R20
305/50R20 is a safe swap for 285/50R20 by the usual ±3% rule: the diameter differs by +2.52%.
Speedometer and odometer
With 305/50R20 on a car calibrated for 285/50R20, the speedometer reads 58.5 mph when you're really doing 60, and the odometer under-counts by 2.5%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.8 mph |
| 45 mph | 46.1 mph |
| 60 mph | 61.5 mph |
| 70 mph | 71.8 mph |
| 80 mph | 82.0 mph |
Other sizes close to 285/50R20
- 285/50R20 vs 275/55R20+2.21%
- 285/50R20 vs 255/50R20-3.78%
- 285/50R20 vs 265/50R20-2.52%
- 285/50R20 vs 275/45R20-4.73%
- 285/50R20 vs 255/55R20-0.57%
- 285/50R20 vs 235/55R20-3.34%
- 285/50R20 vs 255/60R19-0.55%
- 285/50R20 vs 265/60R20+4.16%
- 285/50R20 vs 285/55R20+3.59%
- 285/50R20 vs 275/50R20-1.26%
- 285/50R20 vs 295/55R20+4.98%
- 285/50R20 vs 285/45R21-0.39%
Questions
Can I replace 285/50R20 with 305/50R20?
305/50R20 is a safe swap for 285/50R20 by the usual ±3% rule: the diameter differs by +2.52%.
What's the difference between 285/50R20 and 305/50R20?
305/50R20 is 0.79" taller and 20 mm wider; the sidewall is +0.39". At an indicated 60 mph you'd actually be doing 61.5 mph.
Will 305/50R20 fit on 285/50R20 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.