275/55R19 vs 255/55R20
255/55R20 is a safe swap for 275/55R19 by the usual ±3% rule: the diameter differs by +0.43%.
Speedometer and odometer
With 255/55R20 on a car calibrated for 275/55R19, the speedometer reads 59.7 mph when you're really doing 60, and the odometer under-counts by 0.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.2 mph |
| 60 mph | 60.3 mph |
| 70 mph | 70.3 mph |
| 80 mph | 80.3 mph |
Other sizes close to 275/55R19
Questions
Can I replace 275/55R19 with 255/55R20?
255/55R20 is a safe swap for 275/55R19 by the usual ±3% rule: the diameter differs by +0.43%.
What's the difference between 275/55R19 and 255/55R20?
255/55R20 is 0.13" taller and 20 mm narrower; the sidewall is -0.43". At an indicated 60 mph you'd actually be doing 60.3 mph.
Will 255/55R20 fit on 275/55R19 wheels?
No — 275/55R19 needs a 19" wheel and 255/55R20 a 20" wheel. This is a plus/minus-size swap that changes wheels too.