255/40R19 vs 235/50R18
235/50R18 is a safe swap for 255/40R19 by the usual ±3% rule: the diameter differs by +0.82%.
Speedometer and odometer
With 235/50R18 on a car calibrated for 255/40R19, the speedometer reads 59.5 mph when you're really doing 60, and the odometer under-counts by 0.8%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.2 mph |
| 45 mph | 45.4 mph |
| 60 mph | 60.5 mph |
| 70 mph | 70.6 mph |
| 80 mph | 80.7 mph |
Other sizes close to 255/40R19
- 255/40R19 vs 245/45R19+2.40%
- 255/40R19 vs 245/40R19-1.17%
- 255/40R19 vs 225/50R18-0.64%
- 255/40R19 vs 235/40R19-2.33%
- 255/40R19 vs 255/35R19-3.71%
- 255/40R19 vs 255/45R19+3.71%
- 255/40R19 vs 275/35R19-1.67%
- 255/40R19 vs 275/40R19+2.33%
- 255/40R19 vs 245/35R19-4.73%
- 255/40R19 vs 255/35R20-0.01%
- 255/40R19 vs 225/40R19-3.50%
- 255/40R19 vs 225/45R19-0.22%
Questions
Can I replace 255/40R19 with 235/50R18?
235/50R18 is a safe swap for 255/40R19 by the usual ±3% rule: the diameter differs by +0.82%.
What's the difference between 255/40R19 and 235/50R18?
235/50R18 is 0.22" taller and 20 mm narrower; the sidewall is +0.61". At an indicated 60 mph you'd actually be doing 60.5 mph.
Will 235/50R18 fit on 255/40R19 wheels?
No — 255/40R19 needs a 19" wheel and 235/50R18 a 18" wheel. This is a plus/minus-size swap that changes wheels too.