265/55R15 vs 255/55R15
Going from one to the other changes the overall height by -1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/55R15 | 255/55R15 | Change |
|---|---|---|---|
| Overall height | 26.5" | 26.0" | -1.6 % |
| Sidewall | 5.74" | 5.52" | -3.8 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 83.2" | 81.8" | -1.6 % |
| Revs per mile | 762 | 774 | +1.6 % |
| Axle height | 13.24" | 13.02" | -5.5 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 265/55R15. Fit 255/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,836 on the road, so it over-counts by 164. At a true 70 mph the first turns 889 times a minute, the second 903.