215/40R18 vs 255/40R18
255/40R18 is outside the ±3% rule as a replacement for 215/40R18: the diameter differs by +5.09%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/40R18 on a car calibrated for 215/40R18, the speedometer reads 57.1 mph when you're really doing 60, and the odometer under-counts by 5.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.5 mph |
| 45 mph | 47.3 mph |
| 60 mph | 63.1 mph |
| 70 mph | 73.6 mph |
| 80 mph | 84.1 mph |
Other sizes close to 215/40R18
- 215/40R18 vs 225/45R17+0.81%
- 215/40R18 vs 245/40R18+3.81%
- 215/40R18 vs 225/45R18+4.85%
- 215/40R18 vs 225/40R18+1.27%
- 215/40R18 vs 215/45R17-0.62%
- 215/40R18 vs 235/40R18+2.54%
- 215/40R18 vs 255/35R18+1.03%
- 215/40R18 vs 245/40R17-0.22%
- 215/40R18 vs 275/35R18+3.26%
- 215/40R18 vs 265/35R18+2.15%
- 215/40R18 vs 215/45R18+3.42%
- 215/40R18 vs 245/35R18-0.08%
Questions
Can I replace 215/40R18 with 255/40R18?
255/40R18 is outside the ±3% rule as a replacement for 215/40R18: the diameter differs by +5.09%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 215/40R18 and 255/40R18?
255/40R18 is 1.26" taller and 40 mm wider; the sidewall is +0.63". At an indicated 60 mph you'd actually be doing 63.1 mph.
Will 255/40R18 fit on 215/40R18 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.