275/40R18 vs 255/45R18
255/45R18 is a safe swap for 275/40R18 by the usual ±3% rule: the diameter differs by +1.40%.
Speedometer and odometer
With 255/45R18 on a car calibrated for 275/40R18, the speedometer reads 59.2 mph when you're really doing 60, and the odometer under-counts by 1.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.6 mph |
| 60 mph | 60.8 mph |
| 70 mph | 71.0 mph |
| 80 mph | 81.1 mph |
Other sizes close to 275/40R18
- 275/40R18 vs 225/45R18-2.58%
- 275/40R18 vs 245/40R18-3.54%
- 275/40R18 vs 225/55R17+0.31%
- 275/40R18 vs 245/45R18+0.07%
- 275/40R18 vs 235/50R18+2.22%
- 275/40R18 vs 235/45R18-1.26%
- 275/40R18 vs 245/40R19+0.21%
- 275/40R18 vs 235/40R18-4.73%
- 275/40R18 vs 225/50R18+0.74%
- 275/40R18 vs 235/40R19-0.97%
- 275/40R18 vs 225/55R18+4.06%
- 275/40R18 vs 255/40R18-2.36%
Questions
Can I replace 275/40R18 with 255/45R18?
255/45R18 is a safe swap for 275/40R18 by the usual ±3% rule: the diameter differs by +1.40%.
What's the difference between 275/40R18 and 255/45R18?
255/45R18 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 255/45R18 fit on 275/40R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.