245/40R17 vs 285/30R18
285/30R18 is a safe swap for 245/40R17 by the usual ±3% rule: the diameter differs by +0.06%.
Speedometer and odometer
With 285/30R18 on a car calibrated for 245/40R17, the speedometer reads 60.0 mph when you're really doing 60, and the odometer under-counts by 0.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.0 mph |
| 45 mph | 45.0 mph |
| 60 mph | 60.0 mph |
| 70 mph | 70.0 mph |
| 80 mph | 80.1 mph |
Other sizes close to 245/40R17
- 245/40R17 vs 225/45R17+1.04%
- 245/40R17 vs 225/50R17+4.62%
- 245/40R17 vs 205/55R16+0.65%
- 245/40R17 vs 215/45R17-0.40%
- 245/40R17 vs 205/50R17+1.43%
- 245/40R17 vs 215/50R17+3.03%
- 245/40R17 vs 235/45R17+2.47%
- 245/40R17 vs 245/45R17+3.90%
- 245/40R17 vs 205/45R17-1.83%
- 245/40R17 vs 255/40R17+1.27%
- 245/40R17 vs 245/35R18+0.14%
- 245/40R17 vs 225/50R16+0.57%
Questions
Can I replace 245/40R17 with 285/30R18?
285/30R18 is a safe swap for 245/40R17 by the usual ±3% rule: the diameter differs by +0.06%.
What's the difference between 245/40R17 and 285/30R18?
285/30R18 is 0.02" taller and 40 mm wider; the sidewall is -0.49". At an indicated 60 mph you'd actually be doing 60.0 mph.
Will 285/30R18 fit on 245/40R17 wheels?
No — 245/40R17 needs a 17" wheel and 285/30R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.