305/40R20 vs 275/50R20
275/50R20 is outside the ±3% rule as a replacement for 305/40R20: the diameter differs by +4.12%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 275/50R20 on a car calibrated for 305/40R20, the speedometer reads 57.6 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 | 46.9 mph |
| 60 mph | 62.5 mph |
| 70 mph | 72.9 mph |
| 80 mph | 83.3 mph |
Other sizes close to 305/40R20
- 305/40R20 vs 245/45R20-3.12%
- 305/40R20 vs 255/45R20-1.93%
- 305/40R20 vs 255/50R20+1.46%
- 305/40R20 vs 275/40R20-3.19%
- 305/40R20 vs 265/50R20+2.79%
- 305/40R20 vs 245/50R20+0.13%
- 305/40R20 vs 275/45R20+0.47%
- 305/40R20 vs 255/55R20+4.85%
- 305/40R20 vs 235/55R20+1.93%
- 305/40R20 vs 245/55R19+0.01%
- 305/40R20 vs 265/45R20-0.73%
- 305/40R20 vs 265/50R19-0.59%
Questions
Can I replace 305/40R20 with 275/50R20?
275/50R20 is outside the ±3% rule as a replacement for 305/40R20: the diameter differs by +4.12%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 305/40R20 and 275/50R20?
275/50R20 is 1.22" taller and 30 mm narrower; the sidewall is +0.61". At an indicated 60 mph you'd actually be doing 62.5 mph.
Will 275/50R20 fit on 305/40R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 275 mm tire and the fender clearance.