295/70R24 vs 285/75R24
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/70R24 | 285/75R24 | Change |
|---|---|---|---|
| Overall height | 40.3" | 40.8" | +1.4 % |
| Sidewall | 8.13" | 8.42" | +3.5 % |
| Section width | 295 mm | 285 mm | -3.4 % |
| Circumference | 126.5" | 128.3" | +1.4 % |
| Revs per mile | 501 | 494 | -1.4 % |
| Axle height | 20.13" | 20.42" | +7.3 mm |
| Approved rim width | 8.5–11" | 8–10.5" | overlap 8.5–10.5" |
Both are approved on a rim 8.5" to 10.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 295/70R24. Fit 285/75R24 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 | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,142 on the road, so it under-counts by 142. At a true 70 mph the first turns 584 times a minute, the second 576.