225/45R17 vs 225/40R18
225/40R18 is a safe swap for 225/45R17 by the usual ±3% rule: the diameter differs by +0.46%.
Speedometer and odometer
With 225/40R18 on a car calibrated for 225/45R17, the speedometer reads 59.7 mph when you're really doing 60, and the odometer under-counts by 0.5%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.2 mph |
| 60 mph | 60.3 mph |
| 70 mph | 70.3 mph |
| 80 mph | 80.4 mph |
Other sizes close to 225/45R17
- 225/45R17 vs 225/50R17+3.55%
- 225/45R17 vs 205/55R16-0.38%
- 225/45R17 vs 215/45R17-1.42%
- 225/45R17 vs 205/50R17+0.39%
- 225/45R17 vs 215/50R17+1.97%
- 225/45R17 vs 235/45R17+1.42%
- 225/45R17 vs 245/45R17+2.84%
- 225/45R17 vs 255/35R18+0.22%
- 225/45R17 vs 245/40R17-1.02%
- 225/45R17 vs 205/45R17-2.84%
- 225/45R17 vs 255/40R17+0.24%
- 225/45R17 vs 225/50R16-0.46%
Questions
Can I replace 225/45R17 with 225/40R18?
225/40R18 is a safe swap for 225/45R17 by the usual ±3% rule: the diameter differs by +0.46%.
What's the difference between 225/45R17 and 225/40R18?
225/40R18 is 0.11" taller and 0 mm wider; the sidewall is -0.44". At an indicated 60 mph you'd actually be doing 60.3 mph.
Will 225/40R18 fit on 225/45R17 wheels?
No — 225/45R17 needs a 17" wheel and 225/40R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.