245/40R18 vs 225/45R18
225/45R18 is a safe swap for 245/40R18 by the usual ±3% rule: the diameter differs by +1.00%.
Speedometer and odometer
With 225/45R18 on a car calibrated for 245/40R18, the speedometer reads 59.4 mph when you're really doing 60, and the odometer under-counts by 1.0%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.3 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.6 mph |
| 70 mph | 70.7 mph |
| 80 mph | 80.8 mph |
Other sizes close to 245/40R18
- 245/40R18 vs 225/40R18-2.45%
- 245/40R18 vs 225/50R17+0.55%
- 245/40R18 vs 245/45R18+3.75%
- 245/40R18 vs 235/45R18+2.37%
- 245/40R18 vs 235/40R18-1.22%
- 245/40R18 vs 225/50R18+4.44%
- 245/40R18 vs 215/50R17-0.98%
- 245/40R18 vs 245/45R17-0.14%
- 245/40R18 vs 255/35R18-2.68%
- 245/40R18 vs 255/40R18+1.22%
- 245/40R18 vs 245/35R19+0.14%
- 245/40R18 vs 235/35R19-0.93%
Questions
Can I replace 245/40R18 with 225/45R18?
225/45R18 is a safe swap for 245/40R18 by the usual ±3% rule: the diameter differs by +1.00%.
What's the difference between 245/40R18 and 225/45R18?
225/45R18 is 0.26" taller and 20 mm narrower; the sidewall is +0.13". At an indicated 60 mph you'd actually be doing 60.6 mph.
Will 225/45R18 fit on 245/40R18 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.