235/55R17 vs 235/50R18
235/50R18 is a safe swap for 235/55R17 by the usual ±3% rule: the diameter differs by +0.28%.
Speedometer and odometer
With 235/50R18 on a car calibrated for 235/55R17, the speedometer reads 59.8 mph when you're really doing 60, and the odometer under-counts by 0.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.1 mph |
| 45 mph | 45.1 mph |
| 60 mph | 60.2 mph |
| 70 mph | 70.2 mph |
| 80 mph | 80.2 mph |
Other sizes close to 235/55R17
- 235/55R17 vs 225/50R17-4.85%
- 235/55R17 vs 225/55R17-1.59%
- 235/55R17 vs 225/65R17+4.93%
- 235/55R17 vs 215/55R17-3.19%
- 235/55R17 vs 225/60R17+1.67%
- 235/55R17 vs 215/65R16-0.64%
- 235/55R17 vs 235/60R17+3.40%
- 235/55R17 vs 215/65R17+3.04%
- 235/55R17 vs 215/60R17-0.07%
- 235/55R17 vs 235/50R17-3.40%
- 235/55R17 vs 255/45R18-0.52%
- 235/55R17 vs 215/55R18+0.49%
Questions
Can I replace 235/55R17 with 235/50R18?
235/50R18 is a safe swap for 235/55R17 by the usual ±3% rule: the diameter differs by +0.28%.
What's the difference between 235/55R17 and 235/50R18?
235/50R18 is 0.07" taller and 0 mm wider; the sidewall is -0.46". At an indicated 60 mph you'd actually be doing 60.2 mph.
Will 235/50R18 fit on 235/55R17 wheels?
No — 235/55R17 needs a 17" wheel and 235/50R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.