235/40R18 vs 215/50R17
215/50R17 is a safe swap for 235/40R18 by the usual ±3% rule: the diameter differs by +0.25%.
Speedometer and odometer
With 215/50R17 on a car calibrated for 235/40R18, the speedometer reads 59.9 mph when you're really doing 60, and the odometer under-counts by 0.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.1 mph |
| 60 mph | 60.1 mph |
| 70 mph | 70.2 mph |
| 80 mph | 80.2 mph |
Other sizes close to 235/40R18
- 235/40R18 vs 245/40R18+1.24%
- 235/40R18 vs 225/45R18+2.25%
- 235/40R18 vs 225/40R18-1.24%
- 235/40R18 vs 235/45R18+3.64%
- 235/40R18 vs 235/45R17-0.29%
- 235/40R18 vs 255/35R18-1.47%
- 235/40R18 vs 255/40R18+2.48%
- 235/40R18 vs 235/35R19+0.29%
- 235/40R18 vs 275/35R18+0.70%
- 235/40R18 vs 265/35R18-0.39%
- 235/40R18 vs 275/40R18+4.96%
- 235/40R18 vs 215/45R18+0.85%
Questions
Can I replace 235/40R18 with 215/50R17?
215/50R17 is a safe swap for 235/40R18 by the usual ±3% rule: the diameter differs by +0.25%.
What's the difference between 235/40R18 and 215/50R17?
215/50R17 is 0.06" taller and 20 mm narrower; the sidewall is +0.53". At an indicated 60 mph you'd actually be doing 60.1 mph.
Will 215/50R17 fit on 235/40R18 wheels?
No — 235/40R18 needs a 18" wheel and 215/50R17 a 17" wheel. This is a plus/minus-size swap that changes wheels too.