275/35R18 vs 255/40R18
255/40R18 is a safe swap for 275/35R18 by the usual ±3% rule: the diameter differs by +1.77%.
Speedometer and odometer
With 255/40R18 on a car calibrated for 275/35R18, the speedometer reads 59.0 mph when you're really doing 60, and the odometer under-counts by 1.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.5 mph |
| 45 mph | 45.8 mph |
| 60 mph | 61.1 mph |
| 70 mph | 71.2 mph |
| 80 mph | 81.4 mph |
Other sizes close to 275/35R18
- 275/35R18 vs 245/40R18+0.54%
- 275/35R18 vs 225/45R18+1.54%
- 275/35R18 vs 225/40R18-1.92%
- 275/35R18 vs 245/45R18+4.31%
- 275/35R18 vs 235/45R18+2.92%
- 275/35R18 vs 235/40R18-0.69%
- 275/35R18 vs 215/50R17-0.45%
- 275/35R18 vs 235/45R17-0.99%
- 275/35R18 vs 245/45R17+0.40%
- 275/35R18 vs 255/35R18-2.15%
- 275/35R18 vs 245/35R19+0.68%
- 275/35R18 vs 235/35R19-0.40%
Questions
Can I replace 275/35R18 with 255/40R18?
255/40R18 is a safe swap for 275/35R18 by the usual ±3% rule: the diameter differs by +1.77%.
What's the difference between 275/35R18 and 255/40R18?
255/40R18 is 0.45" taller and 20 mm narrower; the sidewall is +0.23". At an indicated 60 mph you'd actually be doing 61.1 mph.
Will 255/40R18 fit on 275/35R18 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.