285/70R24 vs 285/65R24
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/70R24 | 285/65R24 | Change |
|---|---|---|---|
| Overall height | 39.7" | 38.6" | -2.8 % |
| Sidewall | 7.85" | 7.29" | -7.1 % |
| Section width | 285 mm | 285 mm | 0.0 % |
| Circumference | 124.7" | 121.2" | -2.8 % |
| Revs per mile | 508 | 523 | +2.8 % |
| Axle height | 19.85" | 19.29" | -14.3 mm |
| Approved rim width | 8–10.5" | 8–10.5" | overlap 8–10.5" |
Both are approved on a rim 8" 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 285/70R24. Fit 285/65R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,717 on the road, so it over-counts by 283. At a true 70 mph the first turns 593 times a minute, the second 610.