305/50R20 vs 285/60R20
285/60R20 is outside the ±3% rule as a replacement for 305/50R20: the diameter differs by +4.55%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 285/60R20 on a car calibrated for 305/50R20, the speedometer reads 57.4 mph when you're really doing 60, and the odometer under-counts by 4.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.4 mph |
| 45 mph | 47.0 mph |
| 60 mph | 62.7 mph |
| 70 mph | 73.2 mph |
| 80 mph | 83.6 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 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 285/60R20?
285/60R20 is outside the ±3% rule as a replacement for 305/50R20: the diameter differs by +4.55%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 305/50R20 and 285/60R20?
285/60R20 is 1.46" taller and 20 mm narrower; the sidewall is +0.73". At an indicated 60 mph you'd actually be doing 62.7 mph.
Will 285/60R20 fit on 305/50R20 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.