305/75R24.5 vs 295/80R24.5
Going from one to the other changes the overall height by +1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/75R24.5 | 295/80R24.5 | Change |
|---|---|---|---|
| Overall height | 42.5" | 43.1" | +1.3 % |
| Sidewall | 9.01" | 9.29" | +3.2 % |
| Section width | 305 mm | 295 mm | -3.3 % |
| Circumference | 133.6" | 135.3" | +1.3 % |
| Revs per mile | 474 | 468 | -1.3 % |
| Axle height | 21.26" | 21.54" | +7.3 mm |
| Approved rim width | 8.5–11" | 8.5–11" | overlap 8.5–11" |
Both are approved on a rim 8.5" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 305/75R24.5. Fit 295/80R24.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,134 on the road, so it under-counts by 134. At a true 70 mph the first turns 553 times a minute, the second 546.