275/40R18 vs 275/45R18
275/45R18 is outside the ±3% rule as a replacement for 275/40R18: the diameter differs by +4.06%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 275/45R18 on a car calibrated for 275/40R18, 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 | 72.8 mph |
| 80 mph | 83.2 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 275/45R18?
275/45R18 is outside the ±3% rule as a replacement for 275/40R18: the diameter differs by +4.06%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 275/40R18 and 275/45R18?
275/45R18 is 1.08" taller and 0 mm wider; the sidewall is +0.54". At an indicated 60 mph you'd actually be doing 62.4 mph.
Will 275/45R18 fit on 275/40R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 275 mm tire and the fender clearance.