295/70R24.5 vs 275/80R24.5
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 | 295/70R24.5 | 275/80R24.5 | Change |
|---|---|---|---|
| Overall height | 40.8" | 41.8" | +2.6 % |
| Sidewall | 8.13" | 8.66" | +6.5 % |
| Section width | 295 mm | 275 mm | -6.8 % |
| Circumference | 128.1" | 131.4" | +2.6 % |
| Revs per mile | 495 | 482 | -2.6 % |
| Axle height | 20.38" | 20.91" | +13.5 mm |
| Approved rim width | 8.5–11" | 7.5–10" | overlap 8.5–10" |
Both are approved on a rim 8.5" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 295/70R24.5. Fit 275/80R24.5 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 10,261 on the road, so it under-counts by 261. At a true 70 mph the first turns 577 times a minute, the second 563.