255/40R20 vs 235/50R19
235/50R19 is a safe swap for 255/40R20 by the usual ±3% rule: the diameter differs by +0.79%.
Speedometer and odometer
With 235/50R19 on a car calibrated for 255/40R20, 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 | 80.6 mph |
Other sizes close to 255/40R20
- 255/40R20 vs 245/45R20+2.32%
- 255/40R20 vs 255/45R20+3.58%
- 255/40R20 vs 275/40R20+2.25%
- 255/40R20 vs 245/40R20-1.12%
- 255/40R20 vs 255/45R19+0.01%
- 255/40R20 vs 245/35R20-4.56%
- 255/40R20 vs 255/35R20-3.58%
- 255/40R20 vs 275/35R20-1.62%
- 255/40R20 vs 265/45R20+4.85%
- 255/40R20 vs 285/35R20-0.63%
- 255/40R20 vs 315/35R20+2.32%
- 255/40R20 vs 285/30R20-4.63%
Questions
Can I replace 255/40R20 with 235/50R19?
235/50R19 is a safe swap for 255/40R20 by the usual ±3% rule: the diameter differs by +0.79%.
What's the difference between 255/40R20 and 235/50R19?
235/50R19 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 235/50R19 fit on 255/40R20 wheels?
No — 255/40R20 needs a 20" wheel and 235/50R19 a 19" wheel. This is a plus/minus-size swap that changes wheels too.