285/30R20 vs 305/30R20
305/30R20 is a safe swap for 285/30R20 by the usual ±3% rule: the diameter differs by +1.77%.
Speedometer and odometer
With 305/30R20 on a car calibrated for 285/30R20, the speedometer reads 59.0 mph when you're really doing 60, and the odometer under-counts by 1.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.5 mph |
| 45 mph | 45.8 mph |
| 60 mph | 61.1 mph |
| 70 mph | 71.2 mph |
| 80 mph | 81.4 mph |
Other sizes close to 285/30R20
- 285/30R20 vs 245/40R19-0.06%
- 285/30R20 vs 245/40R20+3.68%
- 285/30R20 vs 275/35R19-0.57%
- 285/30R20 vs 245/35R20+0.07%
- 285/30R20 vs 255/35R20+1.10%
- 285/30R20 vs 275/35R20+3.17%
- 285/30R20 vs 255/40R20+4.86%
- 285/30R20 vs 225/45R19+0.90%
- 285/30R20 vs 285/35R19+0.46%
- 285/30R20 vs 285/35R20+4.20%
- 285/30R20 vs 275/30R20-0.88%
- 285/30R20 vs 265/35R20+2.14%
Questions
Can I replace 285/30R20 with 305/30R20?
305/30R20 is a safe swap for 285/30R20 by the usual ±3% rule: the diameter differs by +1.77%.
What's the difference between 285/30R20 and 305/30R20?
305/30R20 is 0.47" taller and 20 mm wider; the sidewall is +0.24". At an indicated 60 mph you'd actually be doing 61.1 mph.
Will 305/30R20 fit on 285/30R20 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.