255/35R18 vs 255/40R18
255/40R18 is outside the ±3% rule as a replacement for 255/35R18: the diameter differs by +4.01%, 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 255/35R18, the speedometer reads 57.7 mph when you're really doing 60, and the odometer under-counts by 4.0%.
| 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 255/35R18
- 255/35R18 vs 225/45R17-0.22%
- 255/35R18 vs 245/40R18+2.75%
- 255/35R18 vs 225/45R18+3.78%
- 255/35R18 vs 225/40R18+0.24%
- 255/35R18 vs 205/50R17+0.17%
- 255/35R18 vs 235/40R18+1.49%
- 255/35R18 vs 275/35R18+2.20%
- 255/35R18 vs 265/35R18+1.10%
- 255/35R18 vs 255/40R17+0.02%
- 255/35R18 vs 215/45R18+2.36%
- 255/35R18 vs 245/35R18-1.10%
- 255/35R18 vs 225/35R19+0.69%
Questions
Can I replace 255/35R18 with 255/40R18?
255/40R18 is outside the ±3% rule as a replacement for 255/35R18: the diameter differs by +4.01%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/35R18 and 255/40R18?
255/40R18 is 1.00" taller and 0 mm wider; the sidewall is +0.50". At an indicated 60 mph you'd actually be doing 62.4 mph.
Will 255/40R18 fit on 255/35R18 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.