255/40R17 vs 225/40R18
225/40R18 is a safe swap for 255/40R17 by the usual ±3% rule: the diameter differs by +0.22%.
Speedometer and odometer
With 225/40R18 on a car calibrated for 255/40R17, 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 255/40R17
- 255/40R17 vs 225/45R17-0.24%
- 255/40R17 vs 225/50R17+3.30%
- 255/40R17 vs 205/55R16-0.61%
- 255/40R17 vs 215/45R17-1.65%
- 255/40R17 vs 205/50R17+0.16%
- 255/40R17 vs 215/50R17+1.73%
- 255/40R17 vs 235/45R17+1.18%
- 255/40R17 vs 245/45R17+2.60%
- 255/40R17 vs 255/35R18-0.02%
- 255/40R17 vs 245/40R17-1.26%
- 255/40R17 vs 205/45R17-3.07%
- 255/40R17 vs 235/50R17+4.88%
Questions
Can I replace 255/40R17 with 225/40R18?
225/40R18 is a safe swap for 255/40R17 by the usual ±3% rule: the diameter differs by +0.22%.
What's the difference between 255/40R17 and 225/40R18?
225/40R18 is 0.06" taller and 30 mm narrower; the sidewall is -0.47". At an indicated 60 mph you'd actually be doing 60.1 mph.
Will 225/40R18 fit on 255/40R17 wheels?
No — 255/40R17 needs a 17" wheel and 225/40R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.