215/45R17 vs 215/40R18
215/40R18 is a safe swap for 215/45R17 by the usual ±3% rule: the diameter differs by +0.62%.
Speedometer and odometer
With 215/40R18 on a car calibrated for 215/45R17, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.6%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.4 mph |
| 80 mph | 80.5 mph |
Other sizes close to 215/45R17
- 215/45R17 vs 225/45R17+1.44%
- 215/45R17 vs 205/50R17+1.84%
- 215/45R17 vs 215/50R17+3.44%
- 215/45R17 vs 235/45R17+2.88%
- 215/45R17 vs 245/45R17+4.32%
- 215/45R17 vs 245/40R17+0.40%
- 215/45R17 vs 205/45R17-1.44%
- 215/45R17 vs 255/40R17+1.68%
- 215/45R17 vs 195/55R16-0.70%
- 215/45R17 vs 245/35R18+0.54%
- 215/45R17 vs 225/50R16+0.98%
- 215/45R17 vs 275/40R17+4.24%
Questions
Can I replace 215/45R17 with 215/40R18?
215/40R18 is a safe swap for 215/45R17 by the usual ±3% rule: the diameter differs by +0.62%.
What's the difference between 215/45R17 and 215/40R18?
215/40R18 is 0.15" taller and 0 mm wider; the sidewall is -0.42". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 215/40R18 fit on 215/45R17 wheels?
No — 215/45R17 needs a 17" wheel and 215/40R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.