275/40R20 vs 255/45R20
255/45R20 is a safe swap for 275/40R20 by the usual ±3% rule: the diameter differs by +1.30%.
Speedometer and odometer
With 255/45R20 on a car calibrated for 275/40R20, the speedometer reads 59.2 mph when you're really doing 60, and the odometer under-counts by 1.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.6 mph |
| 60 mph | 60.8 mph |
| 70 mph | 70.9 mph |
| 80 mph | 81.0 mph |
Other sizes close to 275/40R20
- 275/40R20 vs 245/45R20+0.07%
- 275/40R20 vs 255/50R20+4.81%
- 275/40R20 vs 245/40R20-3.30%
- 275/40R20 vs 245/50R20+3.43%
- 275/40R20 vs 275/45R20+3.78%
- 275/40R20 vs 225/55R19+0.29%
- 275/40R20 vs 255/40R20-2.20%
- 275/40R20 vs 275/35R20-3.78%
- 275/40R20 vs 265/45R20+2.54%
- 275/40R20 vs 285/35R20-2.82%
- 275/40R20 vs 315/35R20+0.07%
- 275/40R20 vs 245/50R19-0.05%
Questions
Can I replace 275/40R20 with 255/45R20?
255/45R20 is a safe swap for 275/40R20 by the usual ±3% rule: the diameter differs by +1.30%.
What's the difference between 275/40R20 and 255/45R20?
255/45R20 is 0.37" taller and 20 mm narrower; the sidewall is +0.19". At an indicated 60 mph you'd actually be doing 60.8 mph.
Will 255/45R20 fit on 275/40R20 wheels?
Both use a 20" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.