265/75R24.5 vs 265/80R24.5
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/75R24.5 | 265/80R24.5 | Change |
|---|---|---|---|
| Overall height | 40.1" | 41.2" | +2.6 % |
| Sidewall | 7.82" | 8.35" | +6.7 % |
| Section width | 265 mm | 265 mm | 0.0 % |
| Circumference | 126.1" | 129.4" | +2.6 % |
| Revs per mile | 502 | 490 | -2.6 % |
| Axle height | 20.07" | 20.60" | +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 265/75R24.5. Fit 265/80R24.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,260 on the road, so it under-counts by 260. At a true 70 mph the first turns 586 times a minute, the second 571.