245/40R18 vs 245/45R18
245/45R18 is outside the ±3% rule as a replacement for 245/40R18: the diameter differs by +3.75%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 245/45R18 on a car calibrated for 245/40R18, the speedometer reads 57.8 mph when you're really doing 60, and the odometer under-counts by 3.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.1 mph |
| 45 mph | 46.7 mph |
| 60 mph | 62.3 mph |
| 70 mph | 72.6 mph |
| 80 mph | 83.0 mph |
Other sizes close to 245/40R18
- 245/40R18 vs 225/45R18+1.00%
- 245/40R18 vs 225/40R18-2.45%
- 245/40R18 vs 225/50R17+0.55%
- 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 245/45R18?
245/45R18 is outside the ±3% rule as a replacement for 245/40R18: the diameter differs by +3.75%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 245/40R18 and 245/45R18?
245/45R18 is 0.96" taller and 0 mm wider; the sidewall is +0.48". At an indicated 60 mph you'd actually be doing 62.3 mph.
Will 245/45R18 fit on 245/40R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 245 mm tire and the fender clearance.