255/65R15 vs 275/60R15
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 | 255/65R15 | 275/60R15 | Change |
|---|---|---|---|
| Overall height | 28.1" | 28.0" | -0.2 % |
| Sidewall | 6.53" | 6.50" | -0.5 % |
| Section width | 255 mm | 275 mm | +7.8 % |
| Circumference | 88.1" | 87.9" | -0.2 % |
| Revs per mile | 719 | 720 | +0.2 % |
| Axle height | 14.03" | 14.00" | -0.8 mm |
| Approved rim width | 7–9.5" | 7.5–10" | 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 255/65R15. Fit 275/60R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.9 mph | -0.1 |
| 70 mph | 69.9 mph | -0.1 |
| 90 mph | 89.8 mph | -0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,979 on the road, so it over-counts by 21. At a true 70 mph the first turns 839 times a minute, the second 841.