255/75R19 vs 245/75R19
Going from one to the other changes the overall height by -1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/75R19 | 245/75R19 | Change |
|---|---|---|---|
| Overall height | 34.1" | 33.5" | -1.7 % |
| Sidewall | 7.53" | 7.23" | -3.9 % |
| Section width | 255 mm | 245 mm | -3.9 % |
| Circumference | 107.0" | 105.1" | -1.7 % |
| Revs per mile | 592 | 603 | +1.7 % |
| Axle height | 17.03" | 16.73" | -7.5 mm |
| Approved rim width | 7–9.5" | 7–9" | overlap 7–9" |
Both are approved on a rim 7" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 255/75R19. Fit 245/75R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,827 on the road, so it over-counts by 173. At a true 70 mph the first turns 691 times a minute, the second 703.