275/40R19 vs 255/45R19
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/40R19 | 255/45R19 | Change |
|---|---|---|---|
| Overall height | 27.7" | 28.0" | +1.4 % |
| Sidewall | 4.33" | 4.52" | +4.3 % |
| Section width | 275 mm | 255 mm | -7.3 % |
| Circumference | 86.9" | 88.1" | +1.4 % |
| Revs per mile | 729 | 719 | -1.4 % |
| Axle height | 13.83" | 14.02" | +4.8 mm |
| Approved rim width | 7.5–10" | 7–9.5" | overlap 7.5–9.5" |
Both are approved on a rim 7.5" to 9.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/40R19. Fit 255/45R19 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 10,135 on the road, so it under-counts by 135. At a true 70 mph the first turns 851 times a minute, the second 839.
What drivers reported
275/40R19 carries 4 complaints. Nobody has filed one naming 255/45R19.