235/55R18 vs 255/55R18
255/55R18 is outside the ±3% rule as a replacement for 235/55R18: the diameter differs by +3.07%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/55R18 on a car calibrated for 235/55R18, the speedometer reads 58.2 mph when you're really doing 60, and the odometer under-counts by 3.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.9 mph |
| 45 mph | 46.4 mph |
| 60 mph | 61.8 mph |
| 70 mph | 72.2 mph |
| 80 mph | 82.5 mph |
Other sizes close to 235/55R18
- 235/55R18 vs 235/60R18+3.28%
- 235/55R18 vs 235/50R18-3.28%
- 235/55R18 vs 225/60R18+1.61%
- 235/55R18 vs 225/50R18-4.68%
- 235/55R18 vs 245/60R18+4.96%
- 235/55R18 vs 225/55R18-1.54%
- 235/55R18 vs 255/45R19-0.50%
- 235/55R18 vs 235/60R17-0.27%
- 235/55R18 vs 215/65R17-0.61%
- 235/55R18 vs 245/50R18-1.89%
- 235/55R18 vs 235/50R19+0.27%
- 235/55R18 vs 255/45R18-4.05%
Questions
Can I replace 235/55R18 with 255/55R18?
255/55R18 is outside the ±3% rule as a replacement for 235/55R18: the diameter differs by +3.07%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 235/55R18 and 255/55R18?
255/55R18 is 0.87" taller and 20 mm wider; the sidewall is +0.43". At an indicated 60 mph you'd actually be doing 61.8 mph.
Will 255/55R18 fit on 235/55R18 wheels?
Both use a 18" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.