325/35R19 vs 345/30R19
Going from one to the other changes the overall height by -2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/35R19 | 345/30R19 | Change |
|---|---|---|---|
| Overall height | 28.0" | 27.1" | -2.9 % |
| Sidewall | 4.48" | 4.07" | -9.0 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 87.8" | 85.3" | -2.9 % |
| Revs per mile | 721 | 743 | +2.9 % |
| Axle height | 13.98" | 13.57" | -10.3 mm |
| Approved rim width | 9–12" | 9.5–12.5" | 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 325/35R19. Fit 345/30R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.4 mph | -2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,711 on the road, so it over-counts by 289. At a true 70 mph the first turns 842 times a minute, the second 867.