255/55R15 vs 265/50R15
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/55R15 | 265/50R15 | Change |
|---|---|---|---|
| Overall height | 26.0" | 25.4" | -2.3 % |
| Sidewall | 5.52" | 5.22" | -5.5 % |
| Section width | 255 mm | 265 mm | +3.9 % |
| Circumference | 81.8" | 79.9" | -2.3 % |
| Revs per mile | 774 | 793 | +2.3 % |
| Axle height | 13.02" | 12.72" | -7.8 mm |
| Approved rim width | 7–9.5" | 7.5–9.5" | 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 255/55R15. Fit 265/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 87.9 mph | -2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,766 on the road, so it over-counts by 234. At a true 70 mph the first turns 903 times a minute, the second 925.