245/35R18 vs 245/40R18
245/40R18 is outside the ±3% rule as a replacement for 245/35R18: the diameter differs by +3.90%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 245/40R18 on a car calibrated for 245/35R18, the speedometer reads 57.7 mph when you're really doing 60, and the odometer under-counts by 3.9%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.2 mph |
| 45 mph | 46.8 mph |
| 60 mph | 62.3 mph |
| 70 mph | 72.7 mph |
| 80 mph | 83.1 mph |
Other sizes close to 245/35R18
- 245/35R18 vs 225/45R17+0.89%
- 245/35R18 vs 225/45R18+4.93%
- 245/35R18 vs 225/40R18+1.35%
- 245/35R18 vs 215/45R17-0.54%
- 245/35R18 vs 235/40R18+2.62%
- 245/35R18 vs 255/35R18+1.11%
- 245/35R18 vs 245/40R17-0.14%
- 245/35R18 vs 275/35R18+3.34%
- 245/35R18 vs 265/35R18+2.23%
- 245/35R18 vs 215/45R18+3.50%
- 245/35R18 vs 215/40R18+0.08%
- 245/35R18 vs 285/35R18+4.45%
Questions
Can I replace 245/35R18 with 245/40R18?
245/40R18 is outside the ±3% rule as a replacement for 245/35R18: the diameter differs by +3.90%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 245/35R18 and 245/40R18?
245/40R18 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 245/40R18 fit on 245/35R18 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.