255/55R18 vs 235/65R18
235/65R18 is outside the ±3% rule as a replacement for 255/55R18: the diameter differs by +3.39%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
Speedometer and odometer
With 235/65R18 on a car calibrated for 255/55R18, 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 255/55R18
- 255/55R18 vs 235/60R18+0.20%
- 255/55R18 vs 235/55R19+0.46%
- 255/55R18 vs 235/55R18-2.98%
- 255/55R18 vs 235/65R17-0.05%
- 255/55R18 vs 225/60R18-1.42%
- 255/55R18 vs 255/50R19-0.01%
- 255/55R18 vs 245/60R18+1.83%
- 255/55R18 vs 225/55R18-4.47%
- 255/55R18 vs 245/50R18-4.81%
- 255/55R18 vs 255/60R18+3.46%
- 255/55R18 vs 245/55R18-1.49%
- 255/55R18 vs 255/60R17+0.01%
Questions
Can I replace 255/55R18 with 235/65R18?
235/65R18 is outside the ±3% rule as a replacement for 255/55R18: the diameter differs by +3.39%, so the speedometer, odometer and ABS calibration will be off and clearance needs checking.
What's the difference between 255/55R18 and 235/65R18?
235/65R18 is 0.98" taller and 20 mm narrower; the sidewall is +0.49". At an indicated 60 mph you'd actually be doing 62.0 mph.
Will 235/65R18 fit on 255/55R18 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.