285/45R19 vs 275/45R19
Going from one to the other changes the overall height by -1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/45R19 | 275/45R19 | Change |
|---|---|---|---|
| Overall height | 29.1" | 28.7" | -1.2 % |
| Sidewall | 5.05" | 4.87" | -3.5 % |
| Section width | 285 mm | 275 mm | -3.5 % |
| Circumference | 91.4" | 90.3" | -1.2 % |
| Revs per mile | 693 | 702 | +1.2 % |
| Axle height | 14.55" | 14.37" | -4.5 mm |
| Approved rim width | 8–10.5" | 7.5–10" | overlap 8–10" |
Both are approved on a rim 8" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/45R19. Fit 275/45R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.9 mph | -1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,878 on the road, so it over-counts by 122. At a true 70 mph the first turns 809 times a minute, the second 819.