255/45R18 vs 235/55R18
235/55R18 is outside the ±3% rule as a replacement for 255/45R18: the diameter differs by +4.22%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 235/55R18 on a car calibrated for 255/45R18, the speedometer reads 57.6 mph when you're really doing 60, and the odometer under-counts by 4.2%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 31.3 mph |
| 45 mph | 46.9 mph |
| 60 mph | 62.5 mph |
| 70 mph | 73.0 mph |
| 80 mph | 83.4 mph |
Other sizes close to 255/45R18
- 255/45R18 vs 225/45R18-3.93%
- 255/45R18 vs 245/40R18-4.88%
- 255/45R18 vs 245/45R18-1.31%
- 255/45R18 vs 235/50R18+0.80%
- 255/45R18 vs 235/45R18-2.62%
- 255/45R18 vs 235/55R17+0.52%
- 255/45R18 vs 225/50R18-0.66%
- 255/45R18 vs 255/40R19-0.01%
- 255/45R18 vs 225/55R18+2.62%
- 255/45R18 vs 255/40R18-3.71%
- 255/45R18 vs 215/60R17+0.45%
- 255/45R18 vs 225/45R19-0.23%
Questions
Can I replace 255/45R18 with 235/55R18?
235/55R18 is outside the ±3% rule as a replacement for 255/45R18: the diameter differs by +4.22%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/45R18 and 235/55R18?
235/55R18 is 1.14" taller and 20 mm narrower; the sidewall is +0.57". At an indicated 60 mph you'd actually be doing 62.5 mph.
Will 235/55R18 fit on 255/45R18 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.