285/35R18 vs 255/40R18
255/40R18 is a safe swap for 285/35R18 by the usual ±3% rule: the diameter differs by +0.69%.
Speedometer and odometer
With 255/40R18 on a car calibrated for 285/35R18, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.5 mph |
| 80 mph | 80.5 mph |
Other sizes close to 285/35R18
- 285/35R18 vs 225/45R18+0.46%
- 285/35R18 vs 245/40R18-0.53%
- 285/35R18 vs 225/40R18-2.97%
- 285/35R18 vs 225/50R17+0.02%
- 285/35R18 vs 245/45R18+3.20%
- 285/35R18 vs 235/45R18+1.83%
- 285/35R18 vs 235/40R18-1.75%
- 285/35R18 vs 225/50R18+3.88%
- 285/35R18 vs 245/45R17-0.67%
- 285/35R18 vs 255/35R19+0.67%
- 285/35R18 vs 255/35R18-3.20%
- 285/35R18 vs 245/35R19-0.40%
Questions
Can I replace 285/35R18 with 255/40R18?
255/40R18 is a safe swap for 285/35R18 by the usual ±3% rule: the diameter differs by +0.69%.
What's the difference between 285/35R18 and 255/40R18?
255/40R18 is 0.18" taller and 30 mm narrower; the sidewall is +0.09". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 255/40R18 fit on 285/35R18 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.