275/60R20 vs 265/60R20
Going from one to the other changes the overall height by -1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/60R20 | 265/60R20 | Change |
|---|---|---|---|
| Overall height | 33.0" | 32.5" | -1.4 % |
| Sidewall | 6.50" | 6.26" | -3.6 % |
| Section width | 275 mm | 265 mm | -3.6 % |
| Circumference | 103.6" | 102.2" | -1.4 % |
| Revs per mile | 611 | 620 | +1.4 % |
| Axle height | 16.50" | 16.26" | -6.0 mm |
| Approved rim width | 7.5–10" | 7.5–9.5" | 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 275/60R20. Fit 265/60R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.0 mph | -1.0 |
| 90 mph | 88.7 mph | -1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,857 on the road, so it over-counts by 143. At a true 70 mph the first turns 713 times a minute, the second 724.