265/75R15 vs 255/75R15
Going from one to the other changes the overall height by -1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/75R15 | 255/75R15 | Change |
|---|---|---|---|
| Overall height | 30.6" | 30.1" | -1.9 % |
| Sidewall | 7.82" | 7.53" | -3.8 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 96.3" | 94.4" | -1.9 % |
| Revs per mile | 658 | 671 | +1.9 % |
| Axle height | 15.32" | 15.03" | -7.5 mm |
| Approved rim width | 7.5–9.5" | 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 265/75R15. Fit 255/75R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,807 on the road, so it over-counts by 193. At a true 70 mph the first turns 768 times a minute, the second 783.