215/40R18 vs 255/35R18
255/35R18 is a safe swap for 215/40R18 by the usual ±3% rule: the diameter differs by +1.03%.
Speedometer and odometer
With 255/35R18 on a car calibrated for 215/40R18, the speedometer reads 59.4 mph when you're really doing 60, and the odometer under-counts by 1.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.5 mph |
| 60 mph | 60.6 mph |
| 70 mph | 70.7 mph |
| 80 mph | 80.8 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 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%
- 215/40R18 vs 285/35R18+4.37%
Questions
Can I replace 215/40R18 with 255/35R18?
255/35R18 is a safe swap for 215/40R18 by the usual ±3% rule: the diameter differs by +1.03%.
What's the difference between 215/40R18 and 255/35R18?
255/35R18 is 0.26" taller and 40 mm wider; the sidewall is +0.13". At an indicated 60 mph you'd actually be doing 60.6 mph.
Will 255/35R18 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.