345/55R19 vs 325/55R19
Going from one to the other changes the overall height by -2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/55R19 | 325/55R19 | Change |
|---|---|---|---|
| Overall height | 33.9" | 33.1" | -2.6 % |
| Sidewall | 7.47" | 7.04" | -5.8 % |
| Section width | 345 mm | 325 mm | -5.8 % |
| Circumference | 106.6" | 103.9" | -2.6 % |
| Revs per mile | 594 | 610 | +2.6 % |
| Axle height | 16.97" | 16.54" | -11.0 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 345/55R19. Fit 325/55R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,745 on the road, so it over-counts by 255. At a true 70 mph the first turns 693 times a minute, the second 711.