265/40R18 vs 255/45R18
255/45R18 is a safe swap for 265/40R18 by the usual ±3% rule: the diameter differs by +2.62%.
Speedometer and odometer
With 255/45R18 on a car calibrated for 265/40R18, the speedometer reads 58.5 mph when you're really doing 60, and the odometer under-counts by 2.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.8 mph |
| 45 mph | 46.2 mph |
| 60 mph | 61.6 mph |
| 70 mph | 71.8 mph |
| 80 mph | 82.1 mph |
Other sizes close to 265/40R18
- 265/40R18 vs 225/45R18-1.42%
- 265/40R18 vs 245/40R18-2.39%
- 265/40R18 vs 225/40R18-4.78%
- 265/40R18 vs 245/45R18+1.27%
- 265/40R18 vs 235/50R18+3.44%
- 265/40R18 vs 235/45R18-0.07%
- 265/40R18 vs 215/55R17-0.13%
- 265/40R18 vs 235/40R18-3.59%
- 265/40R18 vs 225/50R18+1.94%
- 265/40R18 vs 235/40R19+0.21%
- 265/40R18 vs 255/40R18-1.20%
- 265/40R18 vs 275/35R19+0.88%
Questions
Can I replace 265/40R18 with 255/45R18?
255/45R18 is a safe swap for 265/40R18 by the usual ±3% rule: the diameter differs by +2.62%.
What's the difference between 265/40R18 and 255/45R18?
255/45R18 is 0.69" taller and 10 mm narrower; the sidewall is +0.34". At an indicated 60 mph you'd actually be doing 61.6 mph.
Will 255/45R18 fit on 265/40R18 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.