265/80R24.5 vs 265/75R24.5
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/80R24.5 | 265/75R24.5 | Change |
|---|---|---|---|
| Overall height | 41.2" | 40.1" | -2.5 % |
| Sidewall | 8.35" | 7.82" | -6.3 % |
| Section width | 265 mm | 265 mm | 0.0 % |
| Circumference | 129.4" | 126.1" | -2.5 % |
| Revs per mile | 490 | 502 | +2.5 % |
| Axle height | 20.60" | 20.07" | -13.3 mm |
| Approved rim width | 7.5–9.5" | 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 265/80R24.5. Fit 265/75R24.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,747 on the road, so it over-counts by 253. At a true 70 mph the first turns 571 times a minute, the second 586.