265/45R18 vs 275/45R18
Going from one to the other changes the overall height by +1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/45R18 | 275/45R18 | Change |
|---|---|---|---|
| Overall height | 27.4" | 27.7" | +1.3 % |
| Sidewall | 4.69" | 4.87" | +3.8 % |
| Section width | 265 mm | 275 mm | +3.8 % |
| Circumference | 86.0" | 87.2" | +1.3 % |
| Revs per mile | 736 | 727 | -1.3 % |
| Axle height | 13.69" | 13.87" | +4.5 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 265/45R18. Fit 275/45R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,129 on the road, so it under-counts by 129. At a true 70 mph the first turns 859 times a minute, the second 848.