245/30R20 vs 305/25R20
305/25R20 is a safe swap for 245/30R20 by the usual ±3% rule: the diameter differs by +0.84%.
Speedometer and odometer
With 305/25R20 on a car calibrated for 245/30R20, 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 | 30.3 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.6 mph |
| 80 mph | 80.7 mph |
Other sizes close to 245/30R20
- 245/30R20 vs 255/35R19+0.93%
- 245/30R20 vs 245/35R20+3.74%
- 245/30R20 vs 255/35R20+4.81%
- 245/30R20 vs 245/35R19-0.14%
- 245/30R20 vs 285/30R20+3.66%
- 245/30R20 vs 275/30R20+2.75%
- 245/30R20 vs 285/30R19-0.21%
- 245/30R20 vs 235/35R20+2.67%
- 245/30R20 vs 295/30R20+4.58%
- 245/30R20 vs 295/30R19+0.70%
- 245/30R20 vs 265/30R20+1.83%
- 245/30R20 vs 255/30R20+0.92%
Questions
Can I replace 245/30R20 with 305/25R20?
305/25R20 is a safe swap for 245/30R20 by the usual ±3% rule: the diameter differs by +0.84%.
What's the difference between 245/30R20 and 305/25R20?
305/25R20 is 0.22" taller and 60 mm wider; the sidewall is +0.11". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 305/25R20 fit on 245/30R20 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.