235/65R17 vs 255/55R18
255/55R18 is a safe swap for 235/65R17 by the usual ±3% rule: the diameter differs by +0.05%.
Speedometer and odometer
With 255/55R18 on a car calibrated for 235/65R17, the speedometer reads 60.0 mph when you're really doing 60, and the odometer under-counts by 0.1%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.0 mph |
| 45 mph | 45.0 mph |
| 60 mph | 60.0 mph |
| 70 mph | 70.0 mph |
| 80 mph | 80.0 mph |
Other sizes close to 235/65R17
- 235/65R17 vs 235/60R18+0.26%
- 235/65R17 vs 225/65R17-1.76%
- 235/65R17 vs 225/60R17-4.81%
- 235/65R17 vs 245/65R17+1.76%
- 235/65R17 vs 225/75R16+0.90%
- 235/65R17 vs 235/70R16-0.26%
- 235/65R17 vs 235/60R17-3.19%
- 235/65R17 vs 215/65R17-3.53%
- 235/65R17 vs 255/65R17+3.53%
- 235/65R17 vs 235/70R17+3.19%
- 235/65R17 vs 255/65R16+0.08%
- 235/65R17 vs 255/60R17+0.07%
Questions
Can I replace 235/65R17 with 255/55R18?
255/55R18 is a safe swap for 235/65R17 by the usual ±3% rule: the diameter differs by +0.05%.
What's the difference between 235/65R17 and 255/55R18?
255/55R18 is 0.02" taller and 20 mm wider; the sidewall is -0.49". At an indicated 60 mph you'd actually be doing 60.0 mph.
Will 255/55R18 fit on 235/65R17 wheels?
No — 235/65R17 needs a 17" wheel and 255/55R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.