275/60R17 vs 255/65R17
Going from one to the other changes the overall height by +0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/60R17 | 255/65R17 | Change |
|---|---|---|---|
| Overall height | 30.0" | 30.1" | +0.2 % |
| Sidewall | 6.50" | 6.53" | +0.5 % |
| Section width | 275 mm | 255 mm | -7.3 % |
| Circumference | 94.2" | 94.4" | +0.2 % |
| Revs per mile | 672 | 671 | -0.2 % |
| Axle height | 15.00" | 15.03" | +0.8 mm |
| Approved rim width | 7.5–10" | 7–9.5" | overlap 7.5–9.5" |
Both are approved on a rim 7.5" 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 275/60R17. Fit 255/65R17 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 | 70.1 mph | +0.1 |
| 90 mph | 90.2 mph | +0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,020 on the road, so it under-counts by 20. At a true 70 mph the first turns 785 times a minute, the second 783.