285/60R21 vs 265/65R21
Going from one to the other changes the overall height by +0.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/60R21 | 265/65R21 | Change |
|---|---|---|---|
| Overall height | 34.5" | 34.6" | +0.3 % |
| Sidewall | 6.73" | 6.78" | +0.7 % |
| Section width | 285 mm | 265 mm | -7.0 % |
| Circumference | 108.3" | 108.6" | +0.3 % |
| Revs per mile | 585 | 584 | -0.3 % |
| Axle height | 17.23" | 17.28" | +1.3 mm |
| Approved rim width | 8–10.5" | 7.5–9.5" | overlap 8–9.5" |
Both are approved on a rim 8" to 9.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/60R21. Fit 265/65R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.1 mph | +0.1 |
| 70 mph | 70.2 mph | +0.2 |
| 90 mph | 90.3 mph | +0.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,029 on the road, so it under-counts by 29. At a true 70 mph the first turns 683 times a minute, the second 681.