265/55R20 vs 275/55R20
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 | 265/55R20 | 275/55R20 | Change |
|---|---|---|---|
| Overall height | 31.5" | 31.9" | +1.4 % |
| Sidewall | 5.74" | 5.95" | +3.8 % |
| Section width | 265 mm | 275 mm | +3.8 % |
| Circumference | 98.9" | 100.2" | +1.4 % |
| Revs per mile | 641 | 632 | -1.4 % |
| Axle height | 15.74" | 15.95" | +5.5 mm |
| Approved rim width | 7.5–9.5" | 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 265/55R20. Fit 275/55R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,138 on the road, so it under-counts by 138. At a true 70 mph the first turns 748 times a minute, the second 737.