285/55R20 vs 305/55R20
305/55R20 is a safe swap for 285/55R20 by the usual ±3% rule: the diameter differs by +2.68%.
Speedometer and odometer
With 305/55R20 on a car calibrated for 285/55R20, the speedometer reads 58.4 mph when you're really doing 60, and the odometer under-counts by 2.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.8 mph |
| 45 mph | 46.2 mph |
| 60 mph | 61.6 mph |
| 70 mph | 71.9 mph |
| 80 mph | 82.1 mph |
Other sizes close to 285/55R20
- 285/55R20 vs 275/55R20-1.34%
- 285/55R20 vs 275/60R20+2.01%
- 285/55R20 vs 255/55R20-4.02%
- 285/55R20 vs 265/60R20+0.55%
- 285/55R20 vs 285/60R20+3.47%
- 285/55R20 vs 275/50R20-4.69%
- 285/55R20 vs 33x12.50R20+2.03%
- 285/55R20 vs 295/60R20+4.93%
- 285/55R20 vs 295/55R20+1.34%
- 285/55R20 vs 285/50R20-3.47%
- 285/55R20 vs 245/60R20-2.37%
- 285/55R20 vs 305/50R20-1.03%
Questions
Can I replace 285/55R20 with 305/55R20?
305/55R20 is a safe swap for 285/55R20 by the usual ±3% rule: the diameter differs by +2.68%.
What's the difference between 285/55R20 and 305/55R20?
305/55R20 is 0.87" taller and 20 mm wider; the sidewall is +0.43". At an indicated 60 mph you'd actually be doing 61.6 mph.
Will 305/55R20 fit on 285/55R20 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.