315/50R19 vs 325/45R19
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/50R19 | 325/45R19 | Change |
|---|---|---|---|
| Overall height | 31.4" | 30.5" | -2.8 % |
| Sidewall | 6.20" | 5.76" | -7.1 % |
| Section width | 315 mm | 325 mm | +3.2 % |
| Circumference | 98.7" | 95.9" | -2.8 % |
| Revs per mile | 642 | 661 | +2.8 % |
| Axle height | 15.70" | 15.26" | -11.3 mm |
| Approved rim width | 8.5–11.5" | 9–12" | overlap 9–11.5" |
Both are approved on a rim 9" to 11.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 315/50R19. Fit 325/45R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,718 on the road, so it over-counts by 282. At a true 70 mph the first turns 749 times a minute, the second 771.