245/45R17 vs 245/40R18
245/40R18 is a safe swap for 245/45R17 by the usual ±3% rule: the diameter differs by +0.14%.
Speedometer and odometer
With 245/40R18 on a car calibrated for 245/45R17, the speedometer reads 59.9 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 | 45.1 mph |
| 60 mph | 60.1 mph |
| 70 mph | 70.1 mph |
| 80 mph | 80.1 mph |
Other sizes close to 245/45R17
- 245/45R17 vs 225/45R17-2.76%
- 245/45R17 vs 225/50R17+0.69%
- 245/45R17 vs 225/55R17+4.14%
- 245/45R17 vs 215/45R17-4.14%
- 245/45R17 vs 205/50R17-2.38%
- 245/45R17 vs 215/55R17+2.45%
- 245/45R17 vs 215/50R17-0.84%
- 245/45R17 vs 235/45R17-1.38%
- 245/45R17 vs 205/60R16+0.02%
- 245/45R17 vs 245/40R17-3.76%
- 245/45R17 vs 275/35R18-0.40%
- 245/45R17 vs 235/50R17+2.22%
Questions
Can I replace 245/45R17 with 245/40R18?
245/40R18 is a safe swap for 245/45R17 by the usual ±3% rule: the diameter differs by +0.14%.
What's the difference between 245/45R17 and 245/40R18?
245/40R18 is 0.04" taller and 0 mm wider; the sidewall is -0.48". At an indicated 60 mph you'd actually be doing 60.1 mph.
Will 245/40R18 fit on 245/45R17 wheels?
No — 245/45R17 needs a 17" wheel and 245/40R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.