245/60R20 vs 305/55R20
305/55R20 is outside the ±3% rule as a replacement for 245/60R20: the diameter differs by +5.17%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 305/55R20 on a car calibrated for 245/60R20, the speedometer reads 57.0 mph when you're really doing 60, and the odometer under-counts by 5.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.6 mph |
| 45 mph | 47.3 mph |
| 60 mph | 63.1 mph |
| 70 mph | 73.6 mph |
| 80 mph | 84.1 mph |
Other sizes close to 245/60R20
- 245/60R20 vs 275/55R20+1.06%
- 245/60R20 vs 275/60R20+4.49%
- 245/60R20 vs 255/50R20-4.86%
- 245/60R20 vs 265/50R20-3.62%
- 245/60R20 vs 255/55R20-1.68%
- 245/60R20 vs 235/55R20-4.43%
- 245/60R20 vs 265/60R20+2.99%
- 245/60R20 vs 285/55R20+2.43%
- 245/60R20 vs 275/50R20-2.37%
- 245/60R20 vs 33x12.50R20+4.51%
- 245/60R20 vs 295/55R20+3.80%
- 245/60R20 vs 285/50R20-1.12%
Questions
Can I replace 245/60R20 with 305/55R20?
305/55R20 is outside the ±3% rule as a replacement for 245/60R20: the diameter differs by +5.17%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 245/60R20 and 305/55R20?
305/55R20 is 1.63" taller and 60 mm wider; the sidewall is +0.82". At an indicated 60 mph you'd actually be doing 63.1 mph.
Will 305/55R20 fit on 245/60R20 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.