235/65R18 vs 255/65R18
255/65R18 is outside the ±3% rule as a replacement for 235/65R18: the diameter differs by +3.41%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 255/65R18 on a car calibrated for 235/65R18, 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 | 62.0 mph |
| 70 mph | 72.4 mph |
| 80 mph | 82.7 mph |
Other sizes close to 235/65R18
- 235/65R18 vs 235/60R18-3.08%
- 235/65R18 vs 265/60R18+1.64%
- 235/65R18 vs 225/60R18-4.65%
- 235/65R18 vs 245/60R18-1.51%
- 235/65R18 vs 255/55R18-3.28%
- 235/65R18 vs 255/55R19+0.05%
- 235/65R18 vs 255/65R17+0.08%
- 235/65R18 vs 255/60R18+0.07%
- 235/65R18 vs 245/55R18-4.72%
- 235/65R18 vs 285/60R18+4.79%
- 235/65R18 vs 235/70R17-0.25%
- 235/65R18 vs 275/60R18+3.21%
Questions
Can I replace 235/65R18 with 255/65R18?
255/65R18 is outside the ±3% rule as a replacement for 235/65R18: the diameter differs by +3.41%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 235/65R18 and 255/65R18?
255/65R18 is 1.02" taller and 20 mm wider; the sidewall is +0.51". At an indicated 60 mph you'd actually be doing 62.0 mph.
Will 255/65R18 fit on 235/65R18 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.