205/50R17 vs 225/40R18
225/40R18 is a safe swap for 205/50R17 by the usual ±3% rule: the diameter differs by +0.06%.
Speedometer and odometer
With 225/40R18 on a car calibrated for 205/50R17, the speedometer reads 60.0 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 | 45.0 mph |
| 60 mph | 60.0 mph |
| 70 mph | 70.0 mph |
| 80 mph | 80.1 mph |
Other sizes close to 205/50R17
- 205/50R17 vs 225/45R17-0.39%
- 205/50R17 vs 225/50R17+3.14%
- 205/50R17 vs 205/55R16-0.77%
- 205/50R17 vs 215/45R17-1.81%
- 205/50R17 vs 215/55R17+4.95%
- 205/50R17 vs 215/50R17+1.57%
- 205/50R17 vs 235/45R17+1.02%
- 205/50R17 vs 245/45R17+2.43%
- 205/50R17 vs 215/55R16+0.96%
- 205/50R17 vs 255/35R18-0.17%
- 205/50R17 vs 245/40R17-1.41%
- 205/50R17 vs 205/45R17-3.22%
Questions
Can I replace 205/50R17 with 225/40R18?
225/40R18 is a safe swap for 205/50R17 by the usual ±3% rule: the diameter differs by +0.06%.
What's the difference between 205/50R17 and 225/40R18?
225/40R18 is 0.02" taller and 20 mm wider; the sidewall is -0.49". At an indicated 60 mph you'd actually be doing 60.0 mph.
Will 225/40R18 fit on 205/50R17 wheels?
No — 205/50R17 needs a 17" wheel and 225/40R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.