255/60R24 vs 255/65R24
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 | 255/60R24 | 255/65R24 | Change |
|---|---|---|---|
| Overall height | 36.0" | 37.1" | +2.8 % |
| Sidewall | 6.02" | 6.53" | +8.3 % |
| Section width | 255 mm | 255 mm | 0.0 % |
| Circumference | 113.2" | 116.4" | +2.8 % |
| Revs per mile | 559 | 544 | -2.8 % |
| Axle height | 18.02" | 18.53" | +12.8 mm |
| Approved rim width | 7–9.5" | 7–9.5" | overlap 7–9.5" |
Both are approved on a rim 7" 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 255/60R24. Fit 255/65R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,279 on the road, so it under-counts by 279. At a true 70 mph the first turns 653 times a minute, the second 635.