285/35R18 vs 275/40R18
275/40R18 is outside the ±3% rule as a replacement for 285/35R18: the diameter differs by +3.12%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 275/40R18 on a car calibrated for 285/35R18, the speedometer reads 58.2 mph when you're really doing 60, and the odometer under-counts by 3.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.9 mph |
| 45 mph | 46.4 mph |
| 60 mph | 61.9 mph |
| 70 mph | 72.2 mph |
| 80 mph | 82.5 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 255/40R18+0.69%
Questions
Can I replace 285/35R18 with 275/40R18?
275/40R18 is outside the ±3% rule as a replacement for 285/35R18: the diameter differs by +3.12%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 285/35R18 and 275/40R18?
275/40R18 is 0.81" taller and 10 mm narrower; the sidewall is +0.40". At an indicated 60 mph you'd actually be doing 61.9 mph.
Will 275/40R18 fit on 285/35R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 275 mm tire and the fender clearance.