215/50R17 vs 245/40R18
245/40R18 is a safe swap for 215/50R17 by the usual ±3% rule: the diameter differs by +0.99%.
Speedometer and odometer
With 245/40R18 on a car calibrated for 215/50R17, the speedometer reads 59.4 mph when you're really doing 60, and the odometer under-counts by 1.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.6 mph |
| 70 mph | 70.7 mph |
| 80 mph | 80.8 mph |
Other sizes close to 215/50R17
- 215/50R17 vs 225/45R17-1.93%
- 215/50R17 vs 225/50R17+1.55%
- 215/50R17 vs 215/45R17-3.32%
- 215/50R17 vs 205/50R17-1.55%
- 215/50R17 vs 215/55R17+3.32%
- 215/50R17 vs 235/40R18-0.25%
- 215/50R17 vs 235/45R17-0.54%
- 215/50R17 vs 245/45R17+0.85%
- 215/50R17 vs 215/55R16-0.60%
- 215/50R17 vs 205/60R16+0.87%
- 215/50R17 vs 245/40R17-2.94%
- 215/50R17 vs 205/45R17-4.72%
Questions
Can I replace 215/50R17 with 245/40R18?
245/40R18 is a safe swap for 215/50R17 by the usual ±3% rule: the diameter differs by +0.99%.
What's the difference between 215/50R17 and 245/40R18?
245/40R18 is 0.25" taller and 30 mm wider; the sidewall is -0.37". At an indicated 60 mph you'd actually be doing 60.6 mph.
Will 245/40R18 fit on 215/50R17 wheels?
No — 215/50R17 needs a 17" wheel and 245/40R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.