285/65R24 vs 275/65R24
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 | 285/65R24 | 275/65R24 | Change |
|---|---|---|---|
| Overall height | 38.6" | 38.1" | -1.3 % |
| Sidewall | 7.29" | 7.04" | -3.5 % |
| Section width | 285 mm | 275 mm | -3.5 % |
| Circumference | 121.2" | 119.6" | -1.3 % |
| Revs per mile | 523 | 530 | +1.3 % |
| Axle height | 19.29" | 19.04" | -6.5 mm |
| Approved rim width | 8–10.5" | 7.5–10" | overlap 8–10" |
Both are approved on a rim 8" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/65R24. Fit 275/65R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,867 on the road, so it over-counts by 133. At a true 70 mph the first turns 610 times a minute, the second 618.