315/35R17 vs 285/35R18
285/35R18 is a safe swap for 315/35R17 by the usual ±3% rule: the diameter differs by +0.67%.
Speedometer and odometer
With 285/35R18 on a car calibrated for 315/35R17, 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 315/35R17
- 315/35R17 vs 225/45R17-2.76%
- 315/35R17 vs 245/40R18+0.14%
- 315/35R17 vs 225/50R17+0.69%
- 315/35R17 vs 225/55R17+4.14%
- 315/35R17 vs 215/45R17-4.14%
- 315/35R17 vs 205/50R17-2.38%
- 315/35R17 vs 215/55R17+2.45%
- 315/35R17 vs 215/50R17-0.84%
- 315/35R17 vs 235/45R17-1.38%
- 315/35R17 vs 245/45R170.00%
- 315/35R17 vs 205/60R16+0.02%
- 315/35R17 vs 245/40R17-3.76%
Questions
Can I replace 315/35R17 with 285/35R18?
285/35R18 is a safe swap for 315/35R17 by the usual ±3% rule: the diameter differs by +0.67%.
What's the difference between 315/35R17 and 285/35R18?
285/35R18 is 0.17" taller and 30 mm narrower; the sidewall is -0.41". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 285/35R18 fit on 315/35R17 wheels?
No — 315/35R17 needs a 17" wheel and 285/35R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.