285/75R24.5 vs 265/80R24.5
Going from one to the other changes the overall height by -0.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/75R24.5 | 265/80R24.5 | Change |
|---|---|---|---|
| Overall height | 41.3" | 41.2" | -0.3 % |
| Sidewall | 8.42" | 8.35" | -0.8 % |
| Section width | 285 mm | 265 mm | -7.0 % |
| Circumference | 129.8" | 129.4" | -0.3 % |
| Revs per mile | 488 | 490 | +0.3 % |
| Axle height | 20.67" | 20.60" | -1.8 mm |
| Approved rim width | 8–10.5" | 7.5–9.5" | overlap 8–9.5" |
Both are approved on a rim 8" 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 285/75R24.5. Fit 265/80R24.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.8 mph | -0.2 |
| 70 mph | 69.8 mph | -0.2 |
| 90 mph | 89.7 mph | -0.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,967 on the road, so it over-counts by 33. At a true 70 mph the first turns 569 times a minute, the second 571.