245/80R19 vs 255/75R19
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/80R19 | 255/75R19 | Change |
|---|---|---|---|
| Overall height | 34.4" | 34.1" | -1.1 % |
| Sidewall | 7.72" | 7.53" | -2.4 % |
| Section width | 245 mm | 255 mm | +4.1 % |
| Circumference | 108.2" | 107.0" | -1.1 % |
| Revs per mile | 586 | 592 | +1.1 % |
| Axle height | 17.22" | 17.03" | -4.8 mm |
| Approved rim width | 7–9" | 7–9.5" | 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 245/80R19. Fit 255/75R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,891 on the road, so it over-counts by 109. At a true 70 mph the first turns 683 times a minute, the second 691.