285/80R24.5 vs 265/80R24.5
Going from one to the other changes the overall height by -3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/80R24.5 | 265/80R24.5 | Change |
|---|---|---|---|
| Overall height | 42.5" | 41.2" | -3.0 % |
| Sidewall | 8.98" | 8.35" | -7.0 % |
| Section width | 285 mm | 265 mm | -7.0 % |
| Circumference | 133.4" | 129.4" | -3.0 % |
| Revs per mile | 475 | 490 | +3.0 % |
| Axle height | 21.23" | 20.60" | -16.0 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 285/80R24.5. Fit 265/80R24.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 67.9 mph | -2.1 |
| 90 mph | 87.3 mph | -2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,703 on the road, so it over-counts by 297. At a true 70 mph the first turns 554 times a minute, the second 571.