325/30R19 vs 255/40R19
255/40R19 is a safe swap for 325/30R19 by the usual ±3% rule: the diameter differs by +1.33%.
Speedometer and odometer
With 255/40R19 on a car calibrated for 325/30R19, the speedometer reads 59.2 mph when you're really doing 60, and the odometer under-counts by 1.3%.
| Speedo shows | Actual speed |
|---|---|
| 30 mph | 30.4 mph |
| 45 mph | 45.6 mph |
| 60 mph | 60.8 mph |
| 70 mph | 70.9 mph |
| 80 mph | 81.1 mph |
Other sizes close to 325/30R19
- 325/30R19 vs 245/45R18+0.01%
- 325/30R19 vs 245/45R19+3.76%
- 325/30R19 vs 245/40R19+0.15%
- 325/30R19 vs 225/50R18+0.68%
- 325/30R19 vs 235/40R19-1.03%
- 325/30R19 vs 255/35R19-2.44%
- 325/30R19 vs 275/35R19-0.37%
- 325/30R19 vs 275/40R19+3.69%
- 325/30R19 vs 245/35R20+0.28%
- 325/30R19 vs 245/35R19-3.47%
- 325/30R19 vs 225/40R19-2.21%
- 325/30R19 vs 235/35R19-4.50%
Questions
Can I replace 325/30R19 with 255/40R19?
255/40R19 is a safe swap for 325/30R19 by the usual ±3% rule: the diameter differs by +1.33%.
What's the difference between 325/30R19 and 255/40R19?
255/40R19 is 0.35" taller and 70 mm narrower; the sidewall is +0.18". At an indicated 60 mph you'd actually be doing 60.8 mph.
Will 255/40R19 fit on 325/30R19 wheels?
Both use a 19" rim, so the wheel diameter matches; check the wheel's width range for a 255 mm tire and the fender clearance.