265/40R18 vs 235/50R18
235/50R18 is outside the ±3% rule as a replacement for 265/40R18: the diameter differs by +3.44%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 235/50R18 on a car calibrated for 265/40R18, the speedometer reads 58.0 mph when you're really doing 60, and the odometer under-counts by 3.4%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.0 mph |
| 45 mph | 46.5 mph |
| 60 mph | 62.1 mph |
| 70 mph | 72.4 mph |
| 80 mph | 82.7 mph |
Other sizes close to 265/40R18
- 265/40R18 vs 225/45R18-1.42%
- 265/40R18 vs 245/40R18-2.39%
- 265/40R18 vs 225/40R18-4.78%
- 265/40R18 vs 245/45R18+1.27%
- 265/40R18 vs 235/45R18-0.07%
- 265/40R18 vs 215/55R17-0.13%
- 265/40R18 vs 235/40R18-3.59%
- 265/40R18 vs 225/50R18+1.94%
- 265/40R18 vs 235/40R19+0.21%
- 265/40R18 vs 255/40R18-1.20%
- 265/40R18 vs 275/35R19+0.88%
- 265/40R18 vs 225/40R19-0.99%
Questions
Can I replace 265/40R18 with 235/50R18?
235/50R18 is outside the ±3% rule as a replacement for 265/40R18: the diameter differs by +3.44%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 265/40R18 and 235/50R18?
235/50R18 is 0.91" taller and 30 mm narrower; the sidewall is +0.45". At an indicated 60 mph you'd actually be doing 62.1 mph.
Will 235/50R18 fit on 265/40R18 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.