265/75R24 vs 255/75R24
Going from one to the other changes the overall height by -1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/75R24 | 255/75R24 | Change |
|---|---|---|---|
| Overall height | 39.6" | 39.1" | -1.5 % |
| Sidewall | 7.82" | 7.53" | -3.8 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 124.6" | 122.7" | -1.5 % |
| Revs per mile | 509 | 516 | +1.5 % |
| Axle height | 19.82" | 19.53" | -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 265/75R24. Fit 255/75R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.0 mph | -1.0 |
| 90 mph | 88.7 mph | -1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,851 on the road, so it over-counts by 149. At a true 70 mph the first turns 593 times a minute, the second 602.