275/40R18 vs 235/50R18
235/50R18 is a safe swap for 275/40R18 by the usual ±3% rule: the diameter differs by +2.22%.
Speedometer and odometer
With 235/50R18 on a car calibrated for 275/40R18, the speedometer reads 58.7 mph when you're really doing 60, and the odometer under-counts by 2.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.7 mph |
| 45 mph | 46.0 mph |
| 60 mph | 61.3 mph |
| 70 mph | 71.6 mph |
| 80 mph | 81.8 mph |
Other sizes close to 275/40R18
- 275/40R18 vs 225/45R18-2.58%
- 275/40R18 vs 245/40R18-3.54%
- 275/40R18 vs 225/55R17+0.31%
- 275/40R18 vs 245/45R18+0.07%
- 275/40R18 vs 235/45R18-1.26%
- 275/40R18 vs 245/40R19+0.21%
- 275/40R18 vs 235/40R18-4.73%
- 275/40R18 vs 225/50R18+0.74%
- 275/40R18 vs 235/40R19-0.97%
- 275/40R18 vs 225/55R18+4.06%
- 275/40R18 vs 255/40R18-2.36%
- 275/40R18 vs 275/35R19-0.31%
Questions
Can I replace 275/40R18 with 235/50R18?
235/50R18 is a safe swap for 275/40R18 by the usual ±3% rule: the diameter differs by +2.22%.
What's the difference between 275/40R18 and 235/50R18?
235/50R18 is 0.59" taller and 40 mm narrower; the sidewall is +0.30". At an indicated 60 mph you'd actually be doing 61.3 mph.
Will 235/50R18 fit on 275/40R18 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.