225/50R17 vs 255/40R18
255/40R18 is a safe swap for 225/50R17 by the usual ±3% rule: the diameter differs by +0.67%.
Speedometer and odometer
With 255/40R18 on a car calibrated for 225/50R17, the speedometer reads 59.6 mph when you're really doing 60, and the odometer under-counts by 0.7%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.3 mph |
| 60 mph | 60.4 mph |
| 70 mph | 70.5 mph |
| 80 mph | 80.5 mph |
Other sizes close to 225/50R17
- 225/50R17 vs 225/45R17-3.43%
- 225/50R17 vs 225/45R18+0.44%
- 225/50R17 vs 245/40R18-0.55%
- 225/50R17 vs 225/55R17+3.43%
- 225/50R17 vs 215/45R17-4.80%
- 225/50R17 vs 205/50R17-3.05%
- 225/50R17 vs 215/55R17+1.75%
- 225/50R17 vs 215/50R17-1.52%
- 225/50R17 vs 235/45R17-2.06%
- 225/50R17 vs 245/45R17-0.69%
- 225/50R17 vs 205/60R16-0.67%
- 225/50R17 vs 245/40R17-4.42%
Questions
Can I replace 225/50R17 with 255/40R18?
255/40R18 is a safe swap for 225/50R17 by the usual ±3% rule: the diameter differs by +0.67%.
What's the difference between 225/50R17 and 255/40R18?
255/40R18 is 0.17" taller and 30 mm wider; the sidewall is -0.41". At an indicated 60 mph you'd actually be doing 60.4 mph.
Will 255/40R18 fit on 225/50R17 wheels?
No — 225/50R17 needs a 17" wheel and 255/40R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.