285/30R18 vs 225/40R18
225/40R18 is a safe swap for 285/30R18 by the usual ±3% rule: the diameter differs by +1.43%.
Speedometer and odometer
With 225/40R18 on a car calibrated for 285/30R18, the speedometer reads 59.2 mph when you're really doing 60, and the odometer under-counts by 1.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.6 mph |
| 60 mph | 60.9 mph |
| 70 mph | 71.0 mph |
| 80 mph | 81.1 mph |
Other sizes close to 285/30R18
- 285/30R18 vs 225/45R17+0.97%
- 285/30R18 vs 245/40R18+3.98%
- 285/30R18 vs 215/45R17-0.46%
- 285/30R18 vs 235/40R18+2.71%
- 285/30R18 vs 255/35R18+1.19%
- 285/30R18 vs 245/40R17-0.06%
- 285/30R18 vs 275/35R18+3.42%
- 285/30R18 vs 265/35R18+2.31%
- 285/30R18 vs 215/45R18+3.58%
- 285/30R18 vs 245/35R18+0.08%
- 285/30R18 vs 215/40R18+0.16%
- 285/30R18 vs 285/35R18+4.54%
Questions
Can I replace 285/30R18 with 225/40R18?
225/40R18 is a safe swap for 285/30R18 by the usual ±3% rule: the diameter differs by +1.43%.
What's the difference between 285/30R18 and 225/40R18?
225/40R18 is 0.35" taller and 60 mm narrower; the sidewall is +0.18". At an indicated 60 mph you'd actually be doing 60.9 mph.
Will 225/40R18 fit on 285/30R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 225 mm tire and the fender clearance.