225/40R18 vs 235/45R17
235/45R17 is a safe swap for 225/40R18 by the usual ±3% rule: the diameter differs by +0.96%.
Speedometer and odometer
With 235/45R17 on a car calibrated for 225/40R18, 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 225/40R18
- 225/40R18 vs 225/45R17-0.46%
- 225/40R18 vs 245/40R18+2.51%
- 225/40R18 vs 225/45R18+3.53%
- 225/40R18 vs 235/45R18+4.94%
- 225/40R18 vs 205/50R17-0.06%
- 225/40R18 vs 235/40R18+1.26%
- 225/40R18 vs 255/35R18-0.24%
- 225/40R18 vs 255/40R18+3.77%
- 225/40R18 vs 275/35R18+1.96%
- 225/40R18 vs 265/35R18+0.86%
- 225/40R18 vs 255/40R17-0.22%
- 225/40R18 vs 215/45R18+2.12%
Questions
Can I replace 225/40R18 with 235/45R17?
235/45R17 is a safe swap for 225/40R18 by the usual ±3% rule: the diameter differs by +0.96%.
What's the difference between 225/40R18 and 235/45R17?
235/45R17 is 0.24" taller and 10 mm wider; the sidewall is +0.62". At an indicated 60 mph you'd actually be doing 60.6 mph.
Will 235/45R17 fit on 225/40R18 wheels?
No — 225/40R18 needs a 18" wheel and 235/45R17 a 17" wheel. This is a plus/minus-size swap that changes wheels too.