285/30R18 vs 315/30R18
315/30R18 is a safe swap for 285/30R18 by the usual ±3% rule: the diameter differs by +2.87%.
Speedometer and odometer
With 315/30R18 on a car calibrated for 285/30R18, the speedometer reads 58.3 mph when you're really doing 60, and the odometer under-counts by 2.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.9 mph |
| 45 mph | 46.3 mph |
| 60 mph | 61.7 mph |
| 70 mph | 72.0 mph |
| 80 mph | 82.3 mph |
Other sizes close to 285/30R18
- 285/30R18 vs 225/45R17+0.97%
- 285/30R18 vs 245/40R18+3.98%
- 285/30R18 vs 225/40R18+1.43%
- 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%
Questions
Can I replace 285/30R18 with 315/30R18?
315/30R18 is a safe swap for 285/30R18 by the usual ±3% rule: the diameter differs by +2.87%.
What's the difference between 285/30R18 and 315/30R18?
315/30R18 is 0.71" taller and 30 mm wider; the sidewall is +0.35". At an indicated 60 mph you'd actually be doing 61.7 mph.
Will 315/30R18 fit on 285/30R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 315 mm tire and the fender clearance.