345/25R19 vs 325/25R19
Going from one to the other changes the overall height by -1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/25R19 | 325/25R19 | Change |
|---|---|---|---|
| Overall height | 25.8" | 25.4" | -1.5 % |
| Sidewall | 3.40" | 3.20" | -5.8 % |
| Section width | 345 mm | 325 mm | -5.8 % |
| Circumference | 81.0" | 79.8" | -1.5 % |
| Revs per mile | 782 | 794 | +1.5 % |
| Axle height | 12.90" | 12.70" | -5.0 mm |
| Approved rim width | 9.5–12.5" | 9–12" | overlap 9.5–12" |
Both are approved on a rim 9.5" to 12" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 345/25R19. Fit 325/25R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.6 mph | -1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,847 on the road, so it over-counts by 153. At a true 70 mph the first turns 912 times a minute, the second 926.