325/50R19 vs 305/55R19
Going from one to the other changes the overall height by +1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/50R19 | 305/55R19 | Change |
|---|---|---|---|
| Overall height | 31.8" | 32.2" | +1.3 % |
| Sidewall | 6.40" | 6.60" | +3.2 % |
| Section width | 325 mm | 305 mm | -6.2 % |
| Circumference | 99.9" | 101.2" | +1.3 % |
| Revs per mile | 634 | 626 | -1.3 % |
| Axle height | 15.90" | 16.10" | +5.3 mm |
| Approved rim width | 9–12" | 8.5–11" | overlap 9–11" |
Both are approved on a rim 9" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 325/50R19. Fit 305/55R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,130 on the road, so it under-counts by 130. At a true 70 mph the first turns 740 times a minute, the second 731.