245/45R18 vs 225/55R18
225/55R18 is outside the ±3% rule as a replacement for 245/45R18: the diameter differs by +3.98%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 225/55R18 on a car calibrated for 245/45R18, the speedometer reads 57.7 mph when you're really doing 60, and the odometer under-counts by 4.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.2 mph |
| 45 mph | 46.8 mph |
| 60 mph | 62.4 mph |
| 70 mph | 72.8 mph |
| 80 mph | 83.2 mph |
Other sizes close to 245/45R18
- 245/45R18 vs 225/45R18-2.66%
- 245/45R18 vs 245/40R18-3.62%
- 245/45R18 vs 225/55R17+0.24%
- 245/45R18 vs 235/50R18+2.14%
- 245/45R18 vs 235/45R18-1.33%
- 245/45R18 vs 245/40R19+0.13%
- 245/45R18 vs 235/40R18-4.80%
- 245/45R18 vs 225/50R18+0.66%
- 245/45R18 vs 255/40R18-2.43%
- 245/45R18 vs 275/35R19-0.38%
- 245/45R18 vs 245/50R18+3.62%
- 245/45R18 vs 275/35R18-4.13%
Questions
Can I replace 245/45R18 with 225/55R18?
225/55R18 is outside the ±3% rule as a replacement for 245/45R18: the diameter differs by +3.98%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 245/45R18 and 225/55R18?
225/55R18 is 1.06" taller and 20 mm narrower; the sidewall is +0.53". At an indicated 60 mph you'd actually be doing 62.4 mph.
Will 225/55R18 fit on 245/45R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 225 mm tire and the fender clearance.