305/55R20 vs 285/60R20
285/60R20 is a safe swap for 305/55R20 by the usual ±3% rule: the diameter differs by +0.77%.
Speedometer and odometer
With 285/60R20 on a car calibrated for 305/55R20, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.5 mph |
| 80 mph | 80.6 mph |
Other sizes close to 305/55R20
- 305/55R20 vs 275/55R20-3.91%
- 305/55R20 vs 275/60R20-0.65%
- 305/55R20 vs 275/65R20+2.61%
- 305/55R20 vs 265/60R20-2.07%
- 305/55R20 vs 285/55R20-2.61%
- 305/55R20 vs 33x12.50R20-0.63%
- 305/55R20 vs 295/60R20+2.19%
- 305/55R20 vs 295/55R20-1.30%
- 305/55R20 vs 285/65R20+4.15%
- 305/55R20 vs 245/60R20-4.92%
- 305/55R20 vs 305/50R20-3.62%
- 305/55R20 vs 255/60R20-3.50%
Questions
Can I replace 305/55R20 with 285/60R20?
285/60R20 is a safe swap for 305/55R20 by the usual ±3% rule: the diameter differs by +0.77%.
What's the difference between 305/55R20 and 285/60R20?
285/60R20 is 0.26" taller and 20 mm narrower; the sidewall is +0.13". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 285/60R20 fit on 305/55R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 285 mm tire and the fender clearance.