285/65R20 vs 325/60R20
325/60R20 is a safe swap for 285/65R20 by the usual ±3% rule: the diameter differs by +2.22%.
Speedometer and odometer
With 325/60R20 on a car calibrated for 285/65R20, the speedometer reads 58.7 mph when you're really doing 60, and the odometer under-counts by 2.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.7 mph |
| 45 mph | 46.0 mph |
| 60 mph | 61.3 mph |
| 70 mph | 71.6 mph |
| 80 mph | 81.8 mph |
Other sizes close to 285/65R20
Questions
Can I replace 285/65R20 with 325/60R20?
325/60R20 is a safe swap for 285/65R20 by the usual ±3% rule: the diameter differs by +2.22%.
What's the difference between 285/65R20 and 325/60R20?
325/60R20 is 0.77" taller and 40 mm wider; the sidewall is +0.38". At an indicated 60 mph you'd actually be doing 61.3 mph.
Will 325/60R20 fit on 285/65R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 325 mm tire and the fender clearance.