275/55R20 vs 305/55R20
305/55R20 is outside the ±3% rule as a replacement for 275/55R20: the diameter differs by +4.07%, 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 275/55R20, the speedometer reads 57.7 mph when you're really doing 60, and the odometer under-counts by 4.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.2 mph |
| 45 mph | 46.8 mph |
| 60 mph | 62.4 mph |
| 70 mph | 72.9 mph |
| 80 mph | 83.3 mph |
Other sizes close to 275/55R20
- 275/55R20 vs 275/60R20+3.39%
- 275/55R20 vs 265/50R20-4.63%
- 275/55R20 vs 255/55R20-2.71%
- 275/55R20 vs 265/60R20+1.91%
- 275/55R20 vs 285/55R20+1.36%
- 275/55R20 vs 285/60R20+4.87%
- 275/55R20 vs 275/50R20-3.39%
- 275/55R20 vs 33x12.50R20+3.42%
- 275/55R20 vs 295/55R20+2.71%
- 275/55R20 vs 285/50R20-2.16%
- 275/55R20 vs 245/60R20-1.05%
- 275/55R20 vs 305/50R20+0.31%
Questions
Can I replace 275/55R20 with 305/55R20?
305/55R20 is outside the ±3% rule as a replacement for 275/55R20: the diameter differs by +4.07%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 275/55R20 and 305/55R20?
305/55R20 is 1.30" taller and 30 mm wider; the sidewall is +0.65". At an indicated 60 mph you'd actually be doing 62.4 mph.
Will 305/55R20 fit on 275/55R20 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.