225/40R18 vs 235/45R18
235/45R18 is outside the ±3% rule as a replacement for 225/40R18: the diameter differs by +4.94%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 235/45R18 on a car calibrated for 225/40R18, the speedometer reads 57.2 mph when you're really doing 60, and the odometer under-counts by 4.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.5 mph |
| 45 mph | 47.2 mph |
| 60 mph | 63.0 mph |
| 70 mph | 73.5 mph |
| 80 mph | 84.0 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 205/50R17-0.06%
- 225/40R18 vs 235/40R18+1.26%
- 225/40R18 vs 235/45R17+0.96%
- 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 235/45R18?
235/45R18 is outside the ±3% rule as a replacement for 225/40R18: the diameter differs by +4.94%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 225/40R18 and 235/45R18?
235/45R18 is 1.24" taller and 10 mm wider; the sidewall is +0.62". At an indicated 60 mph you'd actually be doing 63.0 mph.
Will 235/45R18 fit on 225/40R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 235 mm tire and the fender clearance.